LIMITED POWER OF ATTORNEY FOR SECTION 16 REPORTING OBLIGATIONS


      The undersigned hereby constitutes and appoints each of Michael D. Grover,
Sonia M. Dumbleton and W. Jack Plants II as the undersigned's true and lawful
attorney-in-fact, and grants each of them full power to act on behalf of the
undersigned and in the undersigned's name, place and stead, for the purpose of
completing and signing, on behalf of the undersigned, any Form 3, Form 4 or Form
5 (including any amendments thereto) required or permitted to be filed by the
undersigned pursuant to Section 16 of the Securities Exchange Act of 1934, as
amended (the "Exchange Act"), with regard to the undersigned's holdings of or
transactions in the securities of Financial Institutions, Inc., and to file such
forms (and amendments thereto) with the Securities and Exchange Commission, and
to do and perform each and every act and thing requisite or necessary to be done
in connection with such forms (and amendments thereto,) as fully and to all
intents and purposes as the undersigned might or could do in person.

      The authority of Michael D. Grover, Sonia M. Dumbleton and W. Jack Plants
II under this Limited Power of Attorney shall continue until the undersigned is
no longer required to file forms under Section 16(a) of the Exchange Act with
regard to the undersigned's holdings of or transactions in the securities of
Financial Institutions, Inc., unless earlier revoked by the undersigned in
writing.

      The undersigned acknowledges that Michael D. Grover, Sonia M. Dumbleton
and W. Jack Plants II are not assuming any of the undersigned's responsibilities
to comply with Section 16 of the Exchange Act.


/s/ Andrew W. Dorn, Jr.
Signature
Name:  Andrew W. Dorn, Jr.
Date:  June 1, 2021