Exhibit 5.1

June 14, 2010

Board of Directors

CNB Financial Corporation

1 South Second Street

P.O. Box 42

Clearfield, Pennsylvania 16830

Ladies and Gentlemen:

We are acting as counsel to CNB Financial Corporation, a Pennsylvania corporation (the “Company”), in connection with the proposed public offering of 2,926,829 shares of common stock, no par value per share, all of which shares (the “Shares”) are to be sold by the Company pursuant to a prospectus supplement dated June 14, 2010 and the accompanying prospectus dated May 28, 2010 (such documents, collectively, the “Prospectus”) that form part of the Company’s effective registration statement on Form S-3 (File No. 333-166111) (the “Registration Statement”). This opinion letter is furnished to you at your request to enable you to fulfill the requirements of Item 601(b)(5) of Regulation S-K, 17 C.F.R. § 229.601(b)(5), in connection with the Registration Statement.

For purposes of this opinion letter, we have examined copies of such agreements, instruments and documents as we have deemed an appropriate basis on which to render the opinions hereinafter expressed. In our examination of the aforesaid documents, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the accuracy and completeness of all documents submitted to us, the authenticity of all original documents, and the conformity to authentic original documents of all documents submitted to us as copies (including telecopies). As to all matters of fact, we have relied on the representations and statements of fact made in the documents so reviewed, and we have not independently established the facts so relied on. This opinion letter is given, and all statements herein are made, in the context of the foregoing.

This opinion letter is based as to matters of law solely on the Pennsylvania Business Corporation Law of 1988. We express no opinion herein as to any other laws, statutes, ordinances, rules, or regulations. As used herein, the term “Pennsylvania Business Corporation Law of 1988” includes the statutory provisions contained therein, all applicable provisions of the Constitution of the Commonwealth of Pennsylvania and reported judicial decisions interpreting these laws.

Based upon, subject to and limited by the foregoing, we are of the opinion that following (i) execution and delivery by the Company of the Underwriting Agreement dated June 14, 2010, by and between the Company and RBC Capital Markets Corporation, as representative of the several underwriters named therein (the “Underwriting Agreement”), (ii) the effectiveness of the Registration Statement, (iii) issuance of the Shares pursuant to the terms of the Underwriting Agreement and in the manner described in the Registration Statement and Prospectus, and (iv) receipt by the Company of the consideration for the Shares specified in the resolutions of the Board of Directors, the Shares will be validly issued, fully paid, and nonassessable.

This opinion letter has been prepared for use in connection with the filing by the Company of a Current Report on Form 8-K, which Form 8-K will be incorporated by reference into the Registration Statement and Prospectus, and speaks as of the date hereof. We assume no obligation to advise you of any changes in the foregoing subsequent to the effective date of the Registration Statement.

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We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the above-described Form 8-K and to the reference to this firm under the caption “Legal Matters” in the Prospectus. In giving this consent, we do not thereby admit that we are an “expert” within the meaning of the Securities Act of 1933, as amended.

Very truly yours,

/s/ HOGAN LOVELLS US LLP

HOGAN LOVELLS US LLP

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