SECOND SUPPLEMENTAL INDENTURE

Exhibit 4.1

SECOND SUPPLEMENTAL INDENTURE

THIS SECOND SUPPLEMENTAL INDENTURE dated as of July 24, 2015 is by and among Wilmington Trust Company, a Delaware trust company, as trustee (herein, together with its successors in interest, the “Trustee”), Wintrust Financial Corporation, an Illinois corporation (“Wintrust”), and Community Financial Shares, Inc., a Maryland corporation (the “Company”), under the Indenture referred to below.

NOW, THEREFORE, in consideration of the premises and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged by the parties hereto, the Trustee, Wintrust and the Company hereby agree as follows:

PRELIMINARY STATEMENTS

The Trustee and the Company, as successor to Community Financial Shares, Inc., a Delaware corporation, are parties to that certain Indenture dated as of June 21, 2007, as supplemented by the First Supplemental Indenture dated as of June 25, 2013 (the “Indenture”), pursuant to which the Company issued U.S. $3,609,000 of its Floating Rate Junior Subordinated Deferrable Interest Debentures due 2037 (the “Debentures”).

As permitted by the terms of the Indenture, pursuant to an Agreement and Plan of Merger, dated as of March 2, 2015 (the “Merger Agreement”), by and among Wintrust, the Company, Wintrust Merger Sub LLC, an Illinois limited liability company and wholly owned subsidiary of Wintrust (“Merger Sub”), simultaneously with the effectiveness of this Second Supplemental Indenture, the Company shall merge (referred to herein for purposes of Article XI of the Indenture as the “Merger”) with and into Merger Sub, with Merger Sub surviving the Merger as the surviving entity. The parties hereto are entering into this Second Supplemental Indenture pursuant to, and in accordance with, Articles IX and XI of the Indenture.

SECTION 1. Definitions. All capitalized terms used herein that are defined in the Indenture, either directly or by reference therein, shall have the respective meanings assigned them in the Indenture except as otherwise provided herein or unless the context otherwise requires.

SECTION 2. Interpretation.

SECTION 3. Assumption of Obligations.

SECTION 4. Representations and Warranties. Wintrust represents and warrants that (a) it has all necessary power and authority to execute and deliver this Second Supplemental Indenture and to perform the Indenture, (b) it is the successor of the Company pursuant to the Merger effected in accordance with applicable law, (c) it is a corporation organized and existing under the laws of Illinois, (d) both immediately before and after giving effect to the Merger and this Second Supplemental Indenture, no Default or Event of Default, and no event which, after notice or lapse of time or both, would become an Event of Default, has occurred and is continuing and (e) this Second Supplemental Indenture is executed and delivered pursuant to Section 9.1(a) and Article XI of the Indenture and does not require the consent of the Securityholders.

SECTION 5. Conditions of Effectiveness. This Second Supplemental Indenture shall become effective simultaneously with the effectiveness of the Merger, provided, however, that:

SECTION 6. Reference to the Indenture.

SECTION 7. Execution in Counterparts. This Second Supplemental Indenture may be executed in any number of counterparts and by different parties hereto in separate counterparts, each of which when so executed and delivered shall be deemed to be an original and all of which when taken together shall constitute but one and the same instrument.

SECTION 8. Governing Law; Binding Effect. This Second Supplemental Indenture shall be governed by and construed in accordance with the laws of the State of New York and shall be binding upon the parties hereto and their respective successors and assigns.

SECTION 9. The Trustee. The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Second Supplemental Indenture or the due execution thereof by the Company or Wintrust. The recitals of fact contained herein shall be taken as the statements solely of the Company or Wintrust, and the Trustee assumes no responsibility for the correctness thereof.

SECTION 10. Addresses of Wintrust and the Trustee. For all purposes of the Indenture, the Trust Agreement, the Guarantee, the Debentures and related documents, the addresses of Wintrust and the Trustee (which Trustee address shall also be the same for Wilmington Trust Company, in its capacities as Institutional Trustee and Delaware Trustee (each as defined in the Trust Agreement)) henceforth shall be as follows or as may be hereafter designated by Wintrust or the Trustee, respectively, in writing:

Wintrust:

Wintrust Financial Corporation

9700 W. Higgins Road, Suite 800

Rosemont, Illinois 60018

Attention:            General Counsel

The Trustee:

Wilmington Trust Company

Rodney Square North

1100 North Market Street

Wilmington, DE 19890

Attention: Corporate Trust Administration

[Signatures on following page]

IN WITNESS WHEREOF, the parties hereto have caused this Second Supplemental Indenture to be duly executed as of the day and year first written above.