Exhibit 5.1

September 29, 2016

First Midwest Bancorp, Inc.,
                             One Pierce Place, Suite 1500,
                                                          Itasca, Illinois 60143.

Ladies and Gentlemen:

We are acting as counsel to First Midwest Bancorp, Inc., a Delaware corporation (the “Company”), in connection with the issuance and delivery of $150,000,000 aggregate principal amount of 5.875% Subordinated Notes due 2026 (the “Notes”). The Company filed with the Securities and Exchange Commission, on September 12, 2016, a registration statement on Form S-3 (File No. 333-213587) (the “Registration Statement”) under the Securities Act of 1933 (the “Act”) relating to the proposed offer and sale of an unspecified principal amount of the Company’s debt securities, including the Notes. The Notes are being issued under an indenture, dated as of September 29, 2016, between the Company and U.S. Bank National Association, as trustee (the “Trustee”), as supplemented by a First Supplemental Indenture, dated as of September 29, 2016, between the Company and the Trustee (together, the “Indenture”).

In rendering this opinion, we have examined the following documents:

1.                                      The Restated Certificate of Incorporation and the Restated By-laws of the Company.

2.                                      The Indenture.

3.                                      Certificates of officers of the Company with respect to the authorization of the Notes, the determination of the terms of the Notes and related matters.

4.                                      A specimen of the Notes.

We also have examined such questions of law as we have considered necessary or appropriate for the purposes of this opinion. Upon the basis of such examination, we advise you that, in our opinion, the Notes constitute valid and legally

binding obligations of the Company, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors’ rights and to general equity principles.

The foregoing opinion is limited to the Federal laws of the United States, the laws of the State of New York and the General Corporation Law of the State of Delaware, and we are expressing no opinion as to the effect of the laws of any other jurisdiction.

In rendering the foregoing opinion, we are not passing upon, and assume no responsibility for, any disclosure in the Registration Statement or any related prospectus or other offering material regarding the Company or the Notes or their offering and sale.

We have relied as to certain matters on information obtained from public officials, officers of the Company and other sources believed by us to be responsible, and we have assumed, without independent verification, that the Indenture has been duly authorized, executed and delivered by the Trustee, that the Notes conform to the specimen thereof examined by us, that the Trustee’s certificate of authentication of the Notes has been manually signed by one of the Trustee’s authorized officers, that the Notes have been delivered against payment as contemplated in the Registration Statement and that the signatures on all documents examined by us are genuine.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement. In giving this consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act.

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