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Filed Pursuant to Rule 424(b)(3)

Registration No. 333-203880

PROXY STATEMENT OF COMMUNITY FINANCIAL SHARES, INC.

PROSPECTUS OF WINTRUST FINANCIAL CORPORATION

Merger and Conversion Proposals — Your Vote Is Important

DEAR COMMUNITY FINANCIAL SHARES, INC. STOCKHOLDERS:

You are cordially invited to attend a special meeting of stockholders of Community Financial Shares, Inc., a Maryland corporation, or CFS, which will be held on July 16, 2015, at 1:00 p.m., local time, at Community Bank-Wheaton/Glen Ellyn, 357 Roosevelt Road, Glen Ellyn, Illinois 60137.

At the meeting, CFS stockholders will be asked to consider and vote upon certain proposals in connection with the agreement and plan of merger, dated as of March 2, 2015, among Wintrust Financial Corporation, an Illinois corporation, or Wintrust, Wintrust Merger Sub LLC,  a wholly-owned subsidiary of Wintrust, or Merger Co., and CFS, which we refer to as the merger agreement, that provides for Wintrust’s acquisition of CFS.  CFS is the parent company of Community Bank—Wheaton/Glen Ellyn, an Illinois state chartered federally insured commercial bank, which we refer to as the Bank.  The acquisition will be effected through the merger of CFS with and into Merger Co.  In addition, the merger agreement provides that the articles supplementary to the articles of incorporation for each series of preferred stock of CFS will be amended prior to the closing to provide for, among other things, the automatic conversion of each share of CFS preferred stock into 100 shares of CFS common stock immediately prior to the effective time of the merger, which we refer to as the preferred stock conversion.  The purpose of the preferred stock conversion is to facilitate the proposed merger transaction by (i) providing holders of CFS preferred stock with a simplified mechanism to receive the amount of the merger consideration to which they are entitled under the terms of the CFS preferred stock and (ii) providing for the extinguishment of the outstanding CFS preferred stock immediately prior to the effective time of the merger.

The aggregate merger consideration paid by Wintrust to CFS stockholders (including holders of CFS preferred stock converted into CFS common stock immediately prior to the effective time of the merger pursuant to the preferred stock conversion) is expected to be approximately $42,375,000, subject to possible downward adjustment as described below.  Assuming that the reference price as described below is between $42.50 and $52.50, approximately 50% of the aggregate merger consideration will be paid in shares of Wintrust common stock, no par value per share, and approximately 50% will be paid in cash.

The exchange ratio used to determine the number of shares of Wintrust common stock that you will be entitled to receive for each share of CFS common stock, par value $0.01 per share, you own will be determined based on the average, calculated for the 10 trading day period ending on the second trading day prior to completion of the merger, of the volume-weighted average price of a share of Wintrust common stock for each trading day during such period, as displayed under the heading “Bloomberg VWAP” on the Bloomberg page for Wintrust, which we refer to as the reference price, subject to a minimum and maximum reference price equal to $42.50 and $52.50, respectively.  The merger consideration may be adjusted downward (i) if the balance sheet delivered to Wintrust by CFS as of the closing date of the merger reflects that CFS stockholders’ equity, as determined pursuant to the merger agreement, is less than $28,250,000 as of the closing date of the merger or (ii) under certain

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circumstances, if CFS fails to or elects not to cure certain defects or objections materially affecting the marketability of title to real property following notice of such defects or objections to CFS by Wintrust or to obtain certain title endorsements to title policies reasonably required by Wintrust.

The merger consideration is subject to downward adjustment as described in this proxy statement/prospectus, and the exchange ratio will not be determined until after the date of the special meeting.  Therefore, at the time of the special meeting, you will not know the precise value of the merger consideration you may receive on the date the merger is completed.

Assuming no adjustment to the merger consideration and that the currently outstanding 10,781,988 shares of CFS common stock and 191,246 shares of CFS preferred stock remain unchanged at the closing, based on a reference price of $50.34, which is equal to the reference price if it were calculated as of May 27, 2015, the latest practicable date prior to the date of this proxy statement/prospectus, the merger consideration that a holder of CFS common stock (including holders of CFS preferred stock converted into CFS common stock immediately prior to the effective time of the merger pursuant to the preferred stock conversion) would be entitled to receive for each share of CFS common stock would be $0.71 in cash and 0.014 shares of Wintrust common stock.  In each case assuming no adjustment to the merger consideration and that the currently outstanding 10,781,988 shares of CFS common stock and 191,246 shares of CFS preferred stock remain unchanged at the closing, if the reference price were equal to the minimum of $42.50, each share of CFS common stock (including shares of CFS common stock issuable upon conversion of CFS preferred stock immediately prior to the effective time of the merger pursuant to the preferred stock conversion) would be converted into the right to receive $0.71 in cash and 0.017 shares of Wintrust common stock, and if the reference price were equal to the maximum of $52.50, each share of CFS common stock (including shares of CFS common stock issuable upon conversion of the CFS preferred stock immediately prior to the effective time of the merger pursuant to the preferred stock conversion) would be converted into the right to receive $0.71 in cash and 0.013 shares of Wintrust common stock.  Assuming no adjustment to the merger consideration and assuming that the reference price is between $42.50 and $52.50, we estimate that Wintrust may issue up to 498,530 shares of Wintrust common stock to CFS stockholders as contemplated by the merger agreement.

Wintrust common stock is traded on the NASDAQ Global Select Market, under the symbol “WTFC.”  The closing price of Wintrust common stock on May 27, 2015 was $50.47 per share.  CFS’s common stock is traded on the over-the-counter market and is quoted on the OTCQB under the symbol “CFIS.”  The closing price of CFS common stock on May 27, 2015 was $1.39 per share.

The merger cannot be completed unless CFS stockholders approve the proposal to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement and the proposals to approve the amendments to the articles supplementary to the articles of incorporation of CFS for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion.  Your board of directors has unanimously approved the merger agreement, the merger and the other transactions contemplated by the merger agreement and recommends that you vote “FOR” the approval of the merger agreement, the merger and the other transactions contemplated by the merger agreement at the special meeting.  Your board of directors also unanimously recommends that you vote “FOR” the proposals to approve amendments to the articles supplementary to the articles of incorporation of CFS for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion, “FOR” the proposal to approve merger-related compensation arrangements with CFS’s named executive officers and “FOR” the proposal to adjourn the special meeting, if necessary or appropriate, to permit further solicitation of proxies in favor of the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion.

Additional information regarding the merger, the merger agreement, the preferred stock conversion, CFS and Wintrust is set forth in the attached proxy statement/prospectus.  This document also serves as the prospectus for up to 498,530 shares of Wintrust common stock that may be issued by Wintrust in connection with the merger.  We urge you to read this entire document carefully, including the section entitled “Risk Factors” beginning on page 27.

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Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be issued under this proxy statement/prospectus or determined if this proxy statement/prospectus is truthful or complete.  Any representation to the contrary is a criminal offense.

The securities to be issued in connection with the merger agreement, the merger and the other transactions contemplated by the merger agreement are not savings or deposit accounts or other obligations of any bank or nonbank subsidiary of any of the parties, and they are not insured by the Federal Deposit Insurance Corporation or any other governmental agency.

This proxy statement/prospectus is dated May 29, 2015, and is first being mailed to CFS stockholders on or about June 5, 2015.

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REFERENCES TO ADDITIONAL INFORMATION

As permitted by the rules of the Securities and Exchange Commission, which we refer to as the SEC, this proxy statement/prospectus incorporates important business and financial information about Wintrust from other documents that are not included in or delivered with this proxy statement/prospectus.  These documents are available to you without charge upon your written or oral request.  You can obtain documents incorporated by reference in this proxy statement/prospectus through the SEC’s website at www.sec.gov or by requesting them in writing or by telephone at the following address and telephone number:

Wintrust Financial Corporation
9700 W. Higgins Road, Suite 800
Rosemont, Illinois 60018
Attention:  Lisa J. Pattis
Executive Vice President, General Counsel and Corporate Secretary
(847) 939-9000

In order to ensure timely delivery of these documents, you should make your request by July 6, 2015 to receive them before the special meeting.

See “Where You Can Find More Information” beginning on page 177.

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COMMUNITY FINANCIAL SHARES, INC.

357 Roosevelt Road
Glen Ellyn, Illinois 60137

Notice of Special Meeting of Stockholders

TO COMMUNITY FINANCIAL SHARES, INC. STOCKHOLDERS:

NOTICE IS HEREBY GIVEN that Community Financial Shares, Inc., a Maryland corporation, or CFS, will hold a special meeting of stockholders on July 16, 2015 at 1:00 p.m., local time, at Community Bank-Wheaton/Glen Ellyn, 357 Roosevelt Road, Glen Ellyn, Illinois 60137.  The purpose of the meeting is to consider and vote on the following matters:

·                  a proposal to approve the agreement and plan of merger, dated as of March 2, 2015, among Wintrust Financial Corporation, an Illinois corporation, or Wintrust, Wintrust Merger Sub LLC, a wholly-owned subsidiary of Wintrust, or Merger Co., and CFS, which we refer to as the merger agreement, the merger of CFS with and into Merger Co. contemplated by the merger agreement and the other transactions contemplated by the merger agreement.  A copy of the merger agreement is included as Annex A to the proxy statement/prospectus accompanying this notice;

·                  a proposal to approve amendments to the articles supplementary to the articles of incorporation of CFS for the Series C Convertible Noncumulative Perpetual Preferred Stock, or Series C Preferred Shares, providing for, among other amendments, the automatic conversion of each Series C Preferred Share into 100 shares of CFS common stock immediately prior to the effective time of the merger.  The purpose of the conversion is to facilitate the proposed merger transaction by (i) providing holders of Series C Preferred Shares with a simplified mechanism to receive the amount of the merger consideration to which they are entitled under the terms of the Series C Preferred Shares and (ii) providing for the extinguishment of the outstanding Series C Preferred Shares immediately prior to the effective time of the merger.  A copy of the amended and restated articles supplementary reflecting the amendments is included as Annex B to the proxy statement/prospectus accompanying this notice;

·                  a proposal to approve amendments to the articles supplementary to the articles of incorporation of CFS for the Series D Convertible Noncumulative Perpetual Preferred Stock, or Series D Preferred Shares, providing for, among other amendments, the automatic conversion of each Series D Preferred Share into 100 shares of CFS common stock immediately prior to the effective time of the merger.  The purpose of the preferred stock conversion is to facilitate the proposed merger transaction by (i) providing holders of the Series D Preferred Shares with a simplified mechanism to receive the amount of the merger consideration to which they are entitled under the terms of the Series D Preferred Shares and (ii) providing for the extinguishment of the outstanding Series D Preferred Shares immediately prior to the effective time of the merger.  A copy of the amended and restated articles supplementary reflecting the amendments is included as Annex C to the proxy statement/prospectus accompanying this notice;

·                  a proposal to approve amendments to the articles supplementary to the articles of incorporation of CFS for the Series E Convertible Noncumulative Perpetual Preferred Stock, or Series E Preferred Shares, providing for, among other amendments, the automatic conversion of each Series E Preferred Share into 100 shares of CFS common stock immediately prior to the effective time of the merger.  The purpose of the preferred stock conversion is to facilitate the proposed merger transaction by (i) providing holders of Series E Preferred Shares with a simplified mechanism to receive the amount of the merger consideration to which they are entitled under the terms of the Series E Preferred Shares

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and (ii) providing for the extinguishment of the outstanding Series E Preferred Shares immediately prior to the effective time of the merger.  A copy of the amended and restated articles supplementary reflecting the amendments is included as Annex D to the proxy statement/prospectus accompanying this notice;

·                  a proposal to approve, on a non-binding, advisory basis, merger-related compensation arrangements with CFS’s named executive officers; and

·                  a proposal to adjourn the special meeting, if necessary or appropriate, to solicit additional proxies in favor of the proposal to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement and the proposals to approve the amendments to the articles supplementary to the articles of incorporation for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion.

Holders of record of CFS common stock, Series C Preferred Shares, Series D Preferred Shares and Series E Preferred Shares at the close of business on May 27, 2015, which we refer to as the record date, are entitled to receive this notice and to vote on one or more of these proposals at the special meeting and any postponements or adjournments thereof.

Approval of the merger requires the affirmative vote at the special meeting of (i) two-thirds of the outstanding shares of CFS common stock and Series C Preferred Shares (holders of Series C Preferred Shares casting the number of votes equal to the maximum number of shares of CFS common stock into which such holder’s Series C Preferred Shares are convertible as of the record date, without regard to any limitation on the conversion of such Series C Preferred Shares contained in the articles supplementary to the articles of incorporation of CFS for the Series C Preferred Shares), voting together as a single class, which we refer to as the outstanding voting securities, and (ii) a majority of the outstanding shares of each of (A) the Series C Preferred Shares, (B) the Series D Preferred Shares and (C) the Series E Preferred Shares.

Approval of the amendment to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion for the Series C Preferred Shares requires the affirmative vote of (i) two-thirds of the outstanding voting securities, (ii) a majority of the outstanding shares of CFS common stock and (iii) a majority of the outstanding Series C Preferred Shares. Approval of the amendment to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion for the Series D Preferred Shares requires the affirmative vote of (i) two-thirds of the outstanding voting securities and (ii) a majority of the outstanding Series D Preferred Shares.  Approval of the amendment to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion for the Series E Preferred Shares requires the affirmative vote of (i) two-thirds of the outstanding voting securities and (ii) a majority of the outstanding Series E Preferred Shares.

Approval of the proposals to approve merger-related compensation arrangements for CFS’s named executive officers and to adjourn the special meeting, if necessary or appropriate, requires, in each case, a majority of all the votes cast by the outstanding voting securities at the special meeting if a quorum is present.  In the absence of a quorum, a majority of the outstanding voting securities present, in person or by proxy, at the special meeting may adjourn the special meeting.

The board of directors of CFS unanimously recommends that you vote “FOR” the proposal to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement.  Your board of directors also unanimously recommends that you vote “FOR” the proposals to approve the amendments to the articles supplementary to the articles of incorporation of CFS for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion, “FOR” the proposal to approve merger-related compensation arrangements with CFS’s named executive officers and “FOR” proposal to adjourn the special meeting to permit further solicitation of proxies in favor of the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion.

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Your vote is important.  To ensure that your shares are voted at the special meeting, please promptly vote via Internet or telephone, or complete, sign and return the proxy form in the enclosed prepaid envelope, whether or not you plan to attend the meeting in person.  Stockholders who attend the special meeting may revoke their proxies and vote in person, if they so desire.

Glen Ellyn, Illinois
May 29, 2015

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QUESTIONS AND ANSWERS ABOUT THE MERGER AGREEMENT, THE MERGER, THE  PREFERRED STOCK CONVERSION AND THE OTHER TRANSACTIONS CONTEMPLATED BY THE MERGER AGREEMENT

Q:                                  What am I being asked to vote on?  What is the proposed transaction?

A:                                   Holders of CFS preferred stock and CFS common stock are being asked to vote on the approval of the merger agreement, dated as of March 2, 2015, among Wintrust Financial Corporation, or Wintrust, Wintrust Merger Sub LLC, or Merger Co., which is a wholly owned subsidiary of Wintrust, and Community Financial Shares, Inc., or CFS, which provides for the acquisition of CFS by Wintrust through the merger of CFS with and into Merger Co., which we refer to as the merger.  Upon completion of the merger, all shares of CFS common stock (including shares of  CFS common stock issuable upon conversion of the CFS preferred stock outstanding immediately prior to the effective time of the merger as described below) will be cancelled, and holders of CFS common stock will become shareholders of Wintrust.

Holders of CFS common stock and CFS preferred stock are also being asked to approve amendments to the articles supplementary to the articles of incorporation for each series of CFS preferred stock which provide for the conversion of CFS preferred stock into shares of CFS common stock immediately prior to the effective time of the merger, which we refer to as the preferred stock conversion.  The purpose of the preferred stock conversion is to facilitate the proposed merger transaction by (i) providing holders of CFS preferred stock with a simplified mechanism to receive the amount of the merger consideration to which they are entitled under the terms of CFS preferred stock and (ii) providing for the extinguishment of the outstanding CFS preferred stock immediately prior to the effective time of the merger.

Holders of CFS common stock and Series C Preferred Shares are also being asked to vote on a proposal to approve, on a non-binding, advisory basis, merger-related compensation arrangements with CFS’s named executive officers and a proposal to adjourn the special meeting, if necessary or appropriate.

Q:                                  What will CFS stockholders be entitled to receive in the merger?

A:                                   If the merger is completed, the shares of CFS common stock that you own immediately before the completion of the merger (including shares of CFS common stock issuable upon conversion of the CFS preferred stock immediately prior to the effective time of the merger pursuant to the preferred stock conversion) will be converted into the right to receive cash and shares of Wintrust common stock (in each case subject to possible adjustment).  The aggregate merger consideration paid by Wintrust to CFS stockholders is intended to be approximately $42,375,000, subject to possible downward adjustment as described below.  The parties intend for approximately 50% of the aggregate merger consideration to be paid in shares of Wintrust common stock and approximately 50% to be paid in cash.

For each of your shares of CFS common stock, you will receive the per share merger consideration to be calculated as set forth in the merger agreement.  The exchange ratio used to determine the number of shares of Wintrust common stock that you will be entitled to receive for each share of CFS common stock you own will be determined based on the average, calculated for the 10 day trading period ending on the second trading day prior to completion of the merger, of the volume-weighted average price of a share of Wintrust common stock for each trading day during such period, as displayed under the heading “Bloomberg VWAP” on the Bloomberg page for Wintrust, which we refer to as the reference price, subject to a minimum and maximum reference price equal to $42.50 and $52.50, respectively.  Assuming no adjustment to the merger consideration and that the currently outstanding 10,781,988 shares of CFS common stock, 119,829 shares of Series C Convertible Noncumulative Perpetual Preferred Stock, or Series C Preferred Shares, 65,427 shares of Series D Convertible Noncumulative Perpetual Preferred Stock, or Series D Preferred Shares, and 5,990 shares of Series E Convertible Noncumulative Perpetual Preferred Stock, or Series E Preferred Shares, remain unchanged at the closing date, and assuming the conversion of each share of CFS preferred stock into 100 shares of CFS common stock immediately prior to completion of the merger pursuant to the preferred stock conversion, based on a reference price of $50.34, which is equal to the reference price if it were calculated as of May 27, 2015, the latest practicable date prior to the

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date of this proxy statement/prospectus, the merger consideration that a holder of CFS common stock (including holders of the shares of CFS preferred stock converted into shares of CFS common stock immediately prior to the effective time of the merger pursuant to the preferred stock conversion) would be entitled to receive for each share of CFS common stock would be $0.71 in cash and 0.014 shares of Wintrust common stock.  In each case assuming no adjustment to the merger consideration and that the currently outstanding 10,781,988 shares of CFS common stock, 119,829 shares of Series C Preferred Shares, 65,427 shares of Series D Preferred Shares and 5,990 shares of Series E Preferred Shares (sometimes referred to in this proxy statement/prospectus collectively as CFS preferred stock) remain unchanged at the closing, and assuming the conversion of each share of CFS preferred stock into 100 shares of CFS common stock immediately prior to the completion of the merger pursuant to the preferred stock conversion, if the reference price were equal to the minimum of $42.50, each share of CFS common stock (including shares of CFS common stock issuable upon conversion of shares of CFS preferred stock immediately prior to the effective time of the merger pursuant to the preferred stock conversion) would be converted into the right to receive $0.71 in cash and 0.017 shares of Wintrust common stock, and if the reference price were equal to the maximum of $52.50, each share of CFS common stock (including shares of CFS common stock issuable upon conversion of the shares of CFS preferred stock immediately prior to the effective time of the merger pursuant to the preferred stock conversion) would be converted into the right to receive $0.71 in cash and 0.013 shares of Wintrust common stock.  For a description of how the per share merger consideration will be calculated, see “The Merger Agreement—Consideration to be received in the merger” on page 94.

In addition, the merger consideration may be adjusted downward (i) if the balance sheet delivered to Wintrust by CFS as of the closing date of the merger reflects that CFS stockholders’ equity, as determined pursuant to the merger agreement, is less than $28,250,000 or (ii) under certain circumstances, if CFS fails to or elects not to cure certain defects or objections materially affecting the marketability of title to real property following notice of such defects or objections to CFS by Wintrust or to obtain certain title endorsements to title policies reasonably required by Wintrust.  For a description of the possible adjustment of the merger consideration, see “The Merger Agreement—Consideration to be received in the merger—Adjustment to merger consideration” on page 96.

Q:                                  What will holders of CFS options be entitled to receive in the merger?

A:                                   In April 2015, each outstanding and unexercised option to acquire a share of CFS common stock, which we refer to as a CFS option, was terminated, cancelled and redeemed by CFS, and no merger consideration will be exchanged therefor.

Q:                                  Why do CFS and Wintrust want to engage in the merger?

A:                                   CFS believes that the merger will achieve the board of directors’ strategic business objectives, including increasing stockholder value, growing the size of the business and enhancing liquidity for CFS’s stockholders, and Wintrust believes that the merger will provide an opportunity to expand and complement its existing market presence in the Wheaton and Glen Ellyn communities.  As a larger company, Wintrust can provide greater capital and resources and efficiencies from integrating the operations of CFS into Wintrust’s existing operations and allow Community Bank—Wheaton/Glen Ellyn, an Illinois state chartered federally insured commercial bank owned by CFS, which we refer to as the Bank, to compete more effectively and to offer a broader array of products and services to better serve its banking customers.  To review the reasons for the merger in more detail, see “The Merger—CFS’s reasons for the merger and recommendation of the board of directors” on page 84 and “The Merger—Wintrust’s reasons for the merger” on page 85.

Q:                                  What does the board of directors recommend?

A:                                   The CFS board of directors unanimously recommends that you vote “FOR” the proposal to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement, “FOR” the proposals to amend the articles supplementary to the articles of incorporation for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion, “FOR” the proposal to

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approve merger-related compensation arrangements with CFS’s named executive officers and “FOR” the proposal to adjourn the special meeting to permit further solicitation of proxies in favor of the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion.  The CFS board of directors has determined that the merger agreement, the merger and the amendments to the articles supplementary to the articles of incorporation of CFS for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion are advisable and in the best interests of CFS.  To review the background and reasons for the merger in greater detail, see “The Merger” beginning on page 63.

Q:                                  What vote is required to approve the merger?

A:                                   The affirmative vote of two-thirds of the outstanding shares of CFS common stock and Series C Preferred Shares (holders of Series C Preferred Shares casting the number of votes equal to the maximum number of shares of CFS common stock into which such holder’s Series C Preferred Shares are convertible as of the record date, without regard to any limitation on the conversion of such Series C Preferred Shares contained in the articles supplementary to the articles of incorporation for the Series C Preferred Shares), voting together as a single class, which we refer to collectively as the outstanding voting securities, is required to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement.  In addition, a majority of the outstanding shares of each of the Series C Preferred Shares, the Series D Preferred Shares and the Series E Preferred Shares is required to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement.  Abstentions and failures to vote have the effect of votes against the approval of the merger agreement, the merger and the other transactions contemplated by the merger agreement.

Even if the merger agreement, the merger and the other transactions contemplated by the merger agreement receive the requisite votes for approval, the merger will not be completed unless CFS stockholders also approve the amendments to the articles supplementary to the articles of incorporation of CFS for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion.

All of the directors and officers of CFS and certain other stockholders of CFS entered into voting agreements pursuant to which they agreed to vote their CFS shares at the special meeting in favor of the merger and any other matter necessary for consummation of the transactions contemplated by the merger agreement (including the amendments to the articles supplementary to the articles of incorporation of CFS for each series of CFS preferred stock providing for, among other matters, the preferred stock conversion).  The shares subject to the voting agreement represent approximately 10.7% of the outstanding shares of CFS common stock, 31.5% of the outstanding voting securities, 50.1% of the outstanding Series C Preferred Shares, 89.1% of the outstanding Series D Preferred Shares and 0% of the outstanding Series E Preferred Shares, each as of May 27, 2015.  No vote of Wintrust’s shareholders is required in connection with the transactions contemplated by the merger agreement. See “The Merger—Interests of certain persons in the merger” on page 89 and “The Merger—Voting agreement” on page 91.

Q:                                  What vote is required to approve the amendments of the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion with respect to the Series C Preferred Shares?

A:                                   The affirmative vote of two-thirds of the outstanding voting securities is required to approve the proposed amendments, collectively referred to as the amendment, to the articles supplementary to the articles of incorporation of CFS with respect to the Series C Preferred Shares.

Additionally, the articles supplementary to the articles of incorporation of CFS for the Series C Preferred Shares require that the proposed amendment thereto be approved by each of (i) a majority of the outstanding Series C Preferred Shares and (ii) a majority of the outstanding shares of common stock.  Abstentions and failures to vote have the effect of votes against the approval of the proposal to approve the

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amendment to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion with respect to the Series C Preferred Shares.

Even if the amendment of the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion with respect to the Series C Preferred Shares receives the requisite votes for approval, the merger and the preferred stock conversion will not be completed unless CFS stockholders also approve the merger agreement, the merger and the other transactions contemplated by the merger agreement and the other amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion.

See “The Merger—Interests of certain persons in the merger” on page 89 and “The Merger—Voting agreement” on page 91 for a description of the voting agreement entered into by all directors and officers of CFS and certain other stockholders of CFS in connection with the proposed merger transaction.

Q:                                  What vote is required to approve the amendments of the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion with respect to the Series D Preferred Shares?

A:                                   The affirmative vote of two-thirds of the outstanding voting securities is required to approve the proposed amendments, collective referred to as the amendment,  to the articles supplementary to the articles of incorporation of CFS with respect to the Series D Preferred Shares.

Additionally, the articles supplementary to the articles of incorporation of CFS for the Series D Preferred Shares require that this proposed amendment be approved by a majority of the outstanding Series D Preferred Shares.  Abstentions and failures to vote have the effect of votes against the approval of the proposal to approve the amendment of the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion with respect to the Series D Preferred Shares.

Even if the amendment of the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion with respect to the Series D Preferred Shares receives the requisite votes for approval, the merger and the preferred stock conversion will not be completed unless CFS stockholders also approve the merger agreement, the merger and the other transactions contemplated by the merger agreement and the other amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion.

See “The Merger—Interests of certain persons in the merger” on page 89 and “The Merger—Voting agreement” on page 91 for a description of the voting agreement entered into by all directors and officers of CFS and certain other stockholders of CFS in connection with the proposed merger transaction.

Q:                                  What vote is required to approve the amendments of the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion with respect to the Series E Preferred Shares?

A:                                   The affirmative vote of two-thirds of the outstanding voting securities is required to approve the proposed amendments, collectively referred to as the amendment, to the articles supplementary to the articles of incorporation of CFS with respect to the Series E Preferred Shares.

Additionally, the articles supplementary to the articles of incorporation of CFS for the Series E Preferred Shares require that this proposed amendments be approved by a majority of the outstanding Series E Preferred Shares.  Abstentions and failures to vote have the effect of votes against the approval of the proposal to approve the amendment of the articles supplementary to the articles of incorporation of CFS

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providing for, among other matters, the preferred stock conversion with respect to the Series E Preferred Shares.

Even if the amendment of the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion with respect to the Series E Preferred Shares receives the requisite votes for approval, the merger and the preferred stock conversion will not be completed unless CFS stockholders also approve the merger agreement, the merger and the other transactions contemplated by the merger agreement and the other amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion.

See “The Merger—Interests of certain persons in the merger” on page 89 and “The Merger—Voting agreement” on page 91 for a description of the voting agreement entered into by all directors and officers of CFS and certain other stockholders of CFS in connection with the proposed merger transaction.

Q:                                  What vote is required to approve the proposal to approve, on a non-binding, advisory basis, merger-related compensation arrangements with CFS’s named executive officers?

A:                                   A majority of all votes cast by the outstanding shares of CFS common stock and Series C Preferred Shares (holders of Series C Preferred Shares casting the number of votes equal to the maximum number of shares of CFS common stock into which such holder’s Series C Preferred Shares are convertible as of the record date, without regard to any limitation on the conversion of such Series C Preferred Shares contained in the articles supplementary to the articles of incorporation of CFS for the Series C Preferred Shares), voting together as a single class, at the special meeting at which a quorum is present is required to approve, on a non-binding, advisory basis, merger-related compensation arrangements with CFS’s named executive officers. Abstentions and failures to vote will have no effect on the approval of the proposal to approve, on a non-binding, advisory basis, merger-related compensation arrangements with CFS’s named executive officers.

Q:                                  What vote is required to approve the proposal to adjourn the special meeting, if necessary or appropriate, to permit further solicitation of proxies in favor of the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion?

A:                                   A majority of the votes cast by of the outstanding shares of common stock and Series C Preferred Shares (holders of shares of such Series C Preferred Shares casting the number of votes equal to the maximum number of shares of CFS common stock into which such holder’s Series C Preferred Shares are convertible as of the record date, without regard to any limitation on the conversion of such Series C Preferred Shares contained in the articles supplementary for the Series C Preferred Shares), voting together as a single class, if a quorum is present at the special meeting, is required to approve the proposal to adjourn the special meeting, if necessary or appropriate, to solicit additional proxies to approve the merger agreement, the merger, the transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion.  In the absence of a quorum, a majority of the outstanding voting securities present in person or by proxy at the special meeting may adjourn the special meeting.  Abstentions and failures to vote will have no effect on the proposal to adjourn the meeting, if necessary or appropriate, to solicit additional proxies in favor of the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation.

Q:                                  What constitutes a quorum for purposes of the special meeting?

A:                                   CFS’s by-laws provide that a majority of the outstanding securities of CFS entitled to vote, represented in person or by proxy, shall constitute a quorum.  Abstentions are treated as present at the meeting for purposes of determining whether a quorum is present.  If you hold your shares in “street name” and do not provide your broker or other nominee with instructions and your broker or other nominee does not submit a

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proxy card or otherwise does not vote because the broker or other nominee lacks discretionary authority to vote the shares, your shares will not be counted for purposes of determining a quorum and they will have the same effect as a vote against the proposal to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement and the proposals to approve the amendments to the articles supplementary to the articles of incorporation of CFS providing for the preferred stock conversion, as the case may be, and will have no effect on the proposal to approve, on a non-binding, advisory basis, merger-related compensation arrangements with CFS’s named executive officers proposal or the proposal to adjourn the special meeting, if necessary or appropriate.

Q:                                  Why is my vote important?

A:                                   CFS stockholders are being asked to approve, among other things, the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion.  Approval of the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion are closing conditions to the merger.  If all of the required stockholder approvals are not obtained, the merger will not occur.  If you do not submit your proxy by mail, telephone or via the Internet, or vote in person at the special meeting, it will be more difficult for CFS to obtain the necessary quorum to hold the special meeting.  In addition, your failure to submit your proxy or attend the special meeting will have the same effect as a vote against the merger agreement, the merger and other transactions contemplated by the merger agreement and the amendments to the articles of supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion and make it more difficult to obtain approval of the merger agreement, the merger and other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion.

Q:                                  What do I need to do now?  How do I vote?

A:                                   You may vote on all matters presented at the special meeting if you own shares of CFS common stock or Series C Preferred Shares of record at the close of business on the record date for the special meeting, May 27, 2015.  You may vote on (i) the proposal to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement and (ii) the proposal to approve an amendment to the articles supplementary to the articles of incorporation of CFS for the Series D Preferred Shares that provides for the conversion of the Series D Preferred Shares into common stock if you own Series D Preferred Shares of record at the close of business on the record date for the special meeting, May 27, 2015.  You may vote on (i) the proposal to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement and (ii) the proposal to approve an amendment to the articles supplementary to the articles of incorporation of CFS for the Series E Preferred Shares that provides for the conversion of the Series E Preferred Shares into common stock if you own Series E Preferred Shares of record at the close of business on the record date for the special meeting, May 27, 2015.

CFS stockholders of record may vote now by proxy by:

·                  completing, signing, dating and returning the enclosed proxy card in the accompanying pre-addressed postage-paid envelope;

·                  calling the toll-free number specified on your proxy card; or

·                  accessing the Internet website specified on your proxy card.

A CFS stockholder has the right to appoint a person (who need not be a stockholder) as proxy holder to attend and act on his, her or its behalf at the special meeting, other than the CFS representatives of management and the CFS board of directors designated in the form of proxy.  The CFS stockholder may

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exercise this right by completing another appropriate form of proxy and delivering the completed proxy in the manner set forth above.

We strongly encourage you to vote using the proxy card provided by CFS.

If you hold shares of CFS in “street name,” which means your shares are held of record by a broker, bank or nominee, you must provide the record holder of your shares with instructions on how to vote your shares.  Please refer to the voting instruction card used by your broker, bank or nominee to see if you may submit voting instructions using the Internet or telephone.

Additionally, you may also vote in person by attending the special meeting.  If you plan to attend the special meeting and wish to vote in person, you will be given a ballot at the special meeting.  Please note, however, that if your shares are held in “street name,” and you wish to vote in person at the special meeting, you must bring a proxy from the record holder of the shares authorizing you to vote at the special meeting. Whether or not you plan to attend the special meeting, you are encouraged to grant your proxy as described in this proxy statement/prospectus.

Q:                                  How will my proxy be voted?

A:                                   If you vote via the Internet or complete, sign, date and mail your proxy form, your proxy will be voted in accordance with your instructions.  If you sign, date and send in your proxy form, but you do not indicate how you want to vote, your proxy will be voted “FOR” the proposal to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement, the proposals to approve the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion and the other proposals in the notice.

Q:                                  Can I revoke my proxy and change my vote?

A:                                   You can revoke your proxy at any time before it is voted at the special meeting by any of the following methods:

·                  Submitting a later-dated proxy by mail.

·                  Sending a written notice of revocation of proxy, prior to the taking of the vote at the meeting, to the Corporate Secretary of CFS at:

Community Financial Shares, Inc.

357 Roosevelt Road

Glen Ellyn, Illinois 60137

Attention: Christopher P. Barton, Secretary

Facsimile: (630) 545-0399

·                  Attending the special meeting and voting in person, although your attendance at the special meeting will not in and of itself revoke your proxy. You must also vote your shares at the meeting.

If your shares are held in the name of a bank, broker or other record holder, you must obtain a proxy, executed in your favor, from the record holder to be able to vote at the annual meeting.  CFS stockholders must contact their broker, bank or other nominee to find out how to do so.

Q:                                  What if I oppose the merger?  Do I have appraisal rights?

A:                                   CFS stockholders who do not vote in favor of approval of the merger and who otherwise comply with all of the procedures of Title 3, Subtitle 2 of the Maryland General Corporation Law, which we refer to as the MGCL, will be entitled to receive payment in cash of the fair value of their shares of CFS common stock, including common stock issued upon conversion of preferred stock into common stock prior to the merger,

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as ultimately determined under the statutory process.  A copy of the relevant sections of the MGCL is attached as Annex E to this document.

Q:                                  What if I oppose the preferred stock conversion?  Do I have appraisal rights?

A:                                   CFS stockholders who do not vote in favor of approval of the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion are not entitled to appraisal rights.

Q:                                  What are the tax consequences of the merger to me?

A:                                   In general, each of the conversion of your shares of CFS common stock into Wintrust common stock in the merger and the automatic conversion of the Series C Preferred Shares, Series D Preferred Shares and Series E Preferred Shares into CFS common stock immediately prior to the effective time of the merger is intended to be tax-free for United States federal income tax purposes.  However, you generally will recognize gain (but not loss) in an amount limited to the amount of cash you receive in the merger.  Additionally, you will recognize gain or loss on any cash that you receive in lieu of fractional shares of Wintrust’s common stock.  You should consult with your tax adviser for the specific tax consequences of the merger to you.  See “The Merger—Material U.S. federal income tax consequences of the merger” on page 85.

Q:                                  When and where is the special meeting?

A:                                   CFS’s special meeting will take place on July 16, 2015, at 1:00 p.m. local time, at Community Bank-Wheaton/Glen Ellyn, 357 Roosevelt Road, Glen Ellyn, Illinois 60137.

Q:                                  Who may attend the meeting?

A:                                   CFS stockholders on the record date may attend the special meeting.  If you are a stockholder of record, you may need to present proof of identification in order to be admitted into the meeting.

Q:                                  Should I send in my stock certificates now?

A:                                   No. After the merger is completed, the exchange agent for the merger will send you a letter of transmittal with instructions informing you how to send in your stock certificates to the exchange agent.  You should use the letter of transmittal to exchange your CFS stock certificates for the merger consideration.  Do not send in your stock certificates with your proxy form.

Q:                                  When is the merger expected to be completed?

A:                                   We will try to complete the merger as soon as reasonably possible.  Before that happens, the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion must be approved by CFS stockholders, and we must obtain the appropriate regulatory approvals.  Assuming stockholders vote to approve the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion, and assuming we obtain the other appropriate approvals and satisfaction or waiver of the other conditions to the closing described in the merger agreement, we expect to complete the merger in the second or third quarter of 2015.  See “The Merger Agreement—Conditions to completion of the merger” on page 108.

Q:                                 Is completion of the merger subject to any conditions besides stockholder approval of the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion?

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A:                                   Yes. The transaction must receive appropriate regulatory approvals, and there are other closing conditions that must be satisfied.  See “The Merger Agreement—Conditions to completion of the merger” on page 108.

Q:                                  Are there risks I should consider in deciding to vote on the approval of the merger agreement, the merger and the other transactions contemplated by the merger agreement, the amendments to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion and other proposals contained in this proxy statement/prospectus?

A:                                   Yes, in evaluating the merger agreement, the merger and the other transactions contemplated by the merger agreement and the amendment to the articles supplementary to the articles of incorporation of CFS providing for, among other matters, the preferred stock conversion, you should read this proxy statement/prospectus carefully, including the factors discussed in the section titled “Risk Factors” beginning on page 27.

Q:                                  Who can answer my other questions?

A:                                   If you have more questions about the merger or how to submit your proxy, or if you need additional copies of this proxy statement/prospectus or the enclosed proxy form, you should contact Christopher P. Barton, CFS’s Corporate Secretary at (630) 545-0900.

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