PURCHASE AGREEMENT

EXHIBIT 2.1

      PURCHASE AGREEMENT

between

FIRST FINANCIAL BANCSHARES, INC.

and

ENTERPRISE FINANCIAL SERVICES CORP

TABLE OF CONTENTS

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EXHIBIT 2.1

STOCK PURCHASE AGREEMENT

      This Stock Purchase Agreement (Agreement) is effective as of February 5, 2008, by and between First Financial Bancshares, Inc., a Kansas corporation, (Buyer), and Enterprise Financial Services Corp, a Delaware corporation, (Seller).

W I T N E S S E T H:

      WHEREAS, Seller is a bank holding company within the meaning of the Bank Holding Company Act of 1956, as amended, and owner of all of the issued and outstanding shares of common stock (the Bank Stock) of the Great American Bank of De Soto, Kansas (the Bank); and

      WHEREAS, Seller desires to sell all of the Bank Stock to Buyer for the consideration and upon the terms and subject to the conditions set forth in this Agreement; and

      WHEREAS, Buyer desires to purchase from Seller all of the Bank Stock for the consideration and upon the terms and subject to the conditions set forth in this Agreement; and

      NOW, THEREFORE, in consideration of the premises and the mutual covenants and agreements herein contained, the parties hereby agree as follows:

ARTICLE I

PURCHASE OF BANK STOCK

      1.1 Sale and Purchase of Bank Stock. Seller agrees to sell, transfer and deliver the Bank Stock to Buyer, and Buyer agrees to purchase, acquire and accept the Bank Stock from Seller, all upon the terms and subject to the conditions set forth in this Agreement.

      1.2 Bank Stock Consideration. The purchase price for the Bank Stock shall be $6,500,000, or such lesser amount as adjusted by the Purchase Consideration Adjustment procedures as set forth below in Section 1.3 below.

      1.3 Purchase Consideration Adjustment. The purchase price shall be reduced by the amount, if any (the Purchase Consideration Adjustment) that: 2.6 times the amount that Bank Capital at Closing is less than $2,500,000; and 2.6 times the amount that the Allowance for Loan and Lease Losses (ALLL) is less than 1% of the Bank’s loan balance at Closing.

      1.4 Real Estate. The Bank owns land (the Property) located at the site of the Bank at 33050 W. 83 ^rd St. in De Soto, Kansas 66018 in Johnson County, Kansas, and real estate improvements, a bank building, banking furniture, fixtures and equipment and other property located on the Property. For purposes of computing the Bank Capital, the Property shall be assigned an amount equal to $1,545,931.13 less normal and customary depreciation through Closing. Seller will provide the Buyer with true and correct copies of all existing title policies related to the Property. As part of its due diligence, the Buyer may obtain, at its cost, a preliminary title report from the Seller’s title company or another title company with respect to the Property. If Buyer objects to any encumbrance in such title report, it may notify the Seller of such objections on or before February 28, 2008. If Buyer delivers such notice, the Seller shall have 10 business days after its receipt of such notice from Buyer to inform the Buyer that Seller wishes to terminate this Agreement or that Seller will cause such encumbrances to be removed or cured.

      1.5 Closing.

      (a) Regulatory Filing Requirements. Buyer shall file regulatory applications requesting approval for acquisition of the Bank with all required bank regulatory agencies needed to transfer the Bank from the Seller to the Buyer which may include: the Federal Deposit Insurance Corporation; the Kansas Office of the State Bank Commissioner; Board of Governors of the Federal Reserve; and Missouri Division of Finance (collectively, the Regulatory Applications), on or before 30 days after the last party has signed this Agreement. If the Regulatory Applications are not filed on or before March 31, 2008, Seller may rescind and void this Agreement with no further obligations being due Buyer from Seller under this Agreement. The Regulatory Applications are considered to have been timely filed when it is filed with the Federal Reserve Board of the Kansas City region, since Buyer believes that regulatory agency will be the primary regulator. Any other applications to the FDIC, Kansas or Missouri, or copies of the Federal Reserve application will be submitted within a reasonable time after the Federal Reserve application has been submitted. To the extent permitted by law, and except for the acquisition of the Claycomo branch by the Seller, as contemplated by this Agreement, the Seller has agreed to cooperate and not take any actions to delay or deny the Buyer from requesting approval of authority to exercise Missouri branching rights from the Missouri Division of Finance.

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      (b) Final Closing. The parties intend to close the transaction as soon as practicable after receipt of all required regulatory approvals, and in no event later than July 31, 2008, unless the parties agree to extend that date. If the required regulatory approvals have not been obtained by July 31, 2008 and Buyer has used best efforts to obtain such approvals (including filing the Regulatory Applications on or before March 31, 2008, responding in a timely fashion to all regulatory requests for additional information, and complying with all provisions of Section 1.5(a)), the parties agree to close the transaction as soon as practicable after receipt of all required regulatory approvals, and in no event later than September 30, 2008.

      1.6 Intentionally Omitted.

      1.7 Due Diligence. The Buyer has conducted its initial due diligence, but may conduct additional due diligence, on reasonable advance notice to Seller, between the final execution of this Agreement and the Closing in order to confirm that the assets, deposits, total capital and other accounts are in existence and at the levels and amounts contemplated by this Agreement, or within reasonable variances, for 45 days after the date of this Agreement. In no event, as part of such diligence or otherwise, shall Buyer or its employees, officers, directors, agents or affiliates contact any Bank customer, supplier or employee without the Seller’s prior written consent.

      1.8 Bank Dividends and Distributions. The Bank may make dividends and distributions as long as the Purchase Consideration Adjustment required under Section 1.3 is made at Closing.

      1.9 Tax Considerations. The Buyer and Seller agree that the Buyer will structure this transaction as a Section 338(h)(10) election whereby the stock purchase is treated as an asset purchase for purposes of the Internal Revenue Code. In that regard, Seller agrees to use its best efforts to cooperate in signing or executing any elections necessary to enable Buyer to make such Section 338(h)(10) election, or to have the benefit of same due to Seller’s execution of said election. The parties will use their best efforts to agree upon the allocation of the purchase price under Section 338 and the related regulations for all federal income tax purposes, provided that if the parties cannot so agree within 30 days after the Closing Date, each shall be free to determine its own allocation and neither shall be bound by any partial or preceding agreement. The Seller will assist in the preparation of the final income tax return or short period return of the Bank provided that Buyer provides access to all information and records necessary for such return. Seller will pay or accrue all taxes attributable to the period ending on the Closing Date and all prior taxable year ends. The Seller and Buyer will cooperate in making the Section 338(h)(10) election on the short period return or any other tax return wherein the Section 338(h)(10) election in properly made. If they have agreed on the allocation of the purchase price, all such tax returns shall be made in accordance with such allocation and neither shall take any position inconsistent with such allocation.

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      1.10 VFW Loans. The Seller has agreed to cause a bank or other qualified lender of its parent corporation or other affiliates to purchase a 75% participation in the two VFW Loans (loan numbers 4019224 and 4132365) included as part of the $3,500,000 in total loans of the Bank.

      1.11 Seller’s Non Compete Agreement.

      (a) Opening of Financial Institutions. Seller and Seller’s subsidiaries are prohibited from opening or operating, directly or indirectly, financial institutions or branches within a 3.5-mile radius of the current Bank location in De Soto, Kansas after the execution of this Agreement and for a period of 5 years from the Closing. Financial institutions and branches shall also be defined to include cash machines, automated teller machines and loan production offices or similar operations or facilities.

      (b) Non-Solicitation. From the execution of this Agreement and through 5 years following the Closing, Seller and Seller’s subsidiaries will not directly or indirectly through another business or person, solicit, entice away, or otherwise knowingly interfere with any employee, customer, vendor, supplier or other similar business relation, or, to Seller’s knowledge, a prospective vendor, prospective customer or other prospective business relation of Buyer or the Bank.

      (c) Employee Affiliates. To the extent required by existing agreements with the Seller or Seller’s subsidiaries, Seller’s affiliates and stockholders owning more than 5% of Seller’s stock, and executive officers and directors, or family members of any such persons, working for such entities, including the Seller’s subsidiaries and affiliates will be bound by the provisions of Sections 1.11(a) and (b).

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ARTICLE II

DEFINITIONS

      2.1 Allowance for Loan and Lease Losses (ALLL). The ALLL shall be defined as that term is defined for banks by FDIC rules and regulations.

      2.2 Bank. The Bank means the Great American Bank located in Johnson County located in De Soto, Kansas, which is a Kansas domestic banking corporation.

      2.3 Bank Capital. Bank Capital means the book value of the Bank determined in accordance with GAAP, as illustrated on Schedule 1.3 . The only assets and liabilities of the Bank at Closing and used to compute Bank Capital will be those classes of assets and liabilities set forth on the attached Schedule 1.3 . Schedule 2.3 lists the securities that, at Closing, will be pledged for those public funds/deposits which require pledged securities. The Buyer shall have 5 days after the date of this Agreement for due diligence to verify the quality and fair market value of such pledged securities. If the Buyer objects to any such securities, the Seller shall have 5 days after receipt of written notice of Buyer's objection to provide cash or other securities meeting Buyer's approval, which shall not be unreasonably withheld.

      2.4 Bank Holding Company Act (BHC Act). The BHC Act is the Bank Holding Company Act of 1956, as amended from time to time and through the date of Closing.

      2.5 Bank Stock. Bank Stock means 100% of all equity or capital stock of the Great American Bank. Seller warrants there is only one class of said Bank Stock outstanding, which is voting common stock.

      2.6 Closing Date. Closing Date means the date of the Closing as defined in this Agreement.

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      2.7 Material Adverse Effect. Material Adverse Effect means any event, change or effect that is materially adverse to the business, assets, liabilities, condition (financial or otherwise), or results of operations of the Bank, taken as a whole, but shall not include (a) the impact of any changes in banking and similar laws of general applicability or interpretations thereof by courts or governmental authorities, (b) changes in GAAP or regulatory accounting requirements applicable to banks or bank holding companies generally, (c) changes in general levels of interest rates or conditions or circumstances that affect the banking industry generally, or (d) commencement of a war, armed hostilities or terrorism directly or indirectly involving the United States of America.

      2.8 Property. Property has the meaning defined in the Agreement.

      2.9 Interpretation. If any definition or term in this Agreement is the subject of a disagreement or potential litigation between the parties, resolution of the definitions and interpretations will be resolved by referring to the rules, regulations and guidelines of the FDIC.

ARTICLE III

REPRESENTATIONS AND WARRANTIES OF BUYER

      3.1 Organization and Authority. Buyer is a corporation duly organized, validly existing and in good standing under the laws of the State of Kansas and will, as soon as practicable after the execution of this Agreement, file its application to acquire the Bank under the provisions of the Bank Holding Company Act of 1956, as amended. Buyer has the corporate power to enter into and perform this Agreement, and the execution, delivery and performance of this Agreement and the consummation of all of the transactions contemplated hereby by Buyer have been duly and fully authorized by its Board of Directors.

      3.2 Valid and Binding Agreement; No Violation. This Agreement has been duly and validly executed and delivered by Buyer and constitutes a valid and binding agreement of Buyer enforceable against Buyer in accordance with its terms, except as limited by applicable bankruptcy, insolvency or other laws affecting the enforcement of creditors’ rights generally. Neither Buyer’s execution and delivery of this Agreement nor the consummation of the transactions contemplated hereby violates, constitutes a breach of or default under, or conflicts with the Articles of Incorporation or Bylaws of Buyer or any agreement, law, regulation, order, judgment or other restriction of any kind or character to which Buyer is a party or by which it or any of its properties is bound.

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      3.3 Governmental Regulation. Buyer has obtained all approvals and holds all licenses, certificates, permits, franchises and rights from all appropriate federal, state or other public authorities necessary for the lawful conduct of its business and ownership of its properties. Buyer has complied in all material respects with all federal, state and local laws, statutes, regulations, ordinances and rules applicable to it, to the conduct of its business or to the ownership of its properties. Buyer is not aware of any reason why the approvals required for its purchase of the Bank Stock will not be received in a timely manner and without the imposition of a condition, restriction or requirement that is unacceptable to Buyer or Seller.

      3.4 Brokers. There is no broker, finder or other person or entity that would have any v