From The Vindicator newspaper:
MERCER, PA.
Friends of the Mercer Area Library are inviting the public to its Centennial Celebration, "Sipping and Savories," from 5:30 to 7:30 p.m. Saturday. The event offers tasting sips of wine from six local wineries and two local wine makers. There will be tastes of chef-prepared foods, music and more. [1]
From personal communication with the librarian on Facebook:
The first official day of the library is July 8, 1916.
I hope that helps. If you need any more information, please let us know. [2]