SHUMAKER WILLIAMS, P.C.
                            3425 SIMPSON FERRY ROAD
                         CAMP HILL, PENNSYLVANIA 17108
                                 (717) 763-1121


                                                 November 11, 1998


Board of Directors
ACNB Corporation
675 Old Harrisburg Road
Gettysburg, PA 17325

                  RE:      Registration Statement on Form S-4
                           Our File No. 742-98

Ladies/Gentlemen:

         In  connection  with the proposed  offering of up to 561,968  shares of
common  stock,  par  value  $2.50  per  share  (the  "Common  Stock"),  by  ACNB
Corporation (the "Company"),  covered by the Company's Registration Statement on
Form S-4 (the  "Registration  Statement") filed with the Securities and Exchange
Commission  under the  Securities  Act of 1933, as amended,  with respect to the
Common Stock, we, as special counsel to the Company, have reviewed:

         1.       Articles of Incorporation of the Company;

         2.       The Bylaws of the Company;

         3.       Resolutions  adopted by the Board of  Directors of the Company
                  relating  to  the  Registration  Statement,  certified  by the
                  Secretary of the Company;

         4.       The Registration Statement; and

         5.       Copies of the certificates representing shares of the 
                  Common Stock.




         Based on our review of the foregoing, it is our opinion that:

          a.   The  Company  has been  duly  incorporated  under the laws of the
               Commonwealth of Pennsylvania  and is validly existing and in good
               standing under the laws of the Commonwealth; and

          b.   The Common Stock covered by the  Registration  Statement has been
               duly  authorized and, when issued pursuant to the terms described
               in the  Registration  Statement,  will be  legally  issued by the
               Company and fully paid and non-assessable.

     We consent to the filing of this opinion as an exhibit to the  Registration
Statement and the reference to us in the related Proxy Statement/Prospectus.  In
giving this consent, we do not thereby admit that we come within the category of
persons whose consent is required under Section 7 of the Securities Act of 1933,
as  amended,  or the  rules  and  regulations  of the  Securities  and  Exchange
Commission thereunder.

                                             Very truly yours,



                                             /s/Shumaker Williams, P.C.
                                             --------------------------
                                             SHUMAKER WILLIAMS, P.C.