Ancestry.com offers a database for American Civil War soldiers and in that I did find Stills but not many in Pennsylvania. One was a Benjamin Still. He enlisted as a Private on 20 April 1861 for Pennsylvania on behalf of the Union. He served in Company I, 4th Infantry Regiment Pennsylvania and was mustered out on 27 Jul 1861 at Harrisburg, PA.
Historical Data Systems, comp.. American Civil War Soldiers [database on-line]. Provo, UT, USA: Ancestry.com Operations Inc, 1999.