Lots of different rules govern where you can camp in PA.
In Delaware Water Gap you must camp within 100' of the trail. http://www.nps.gov/dewa/planyourvisit/upload/sb2at.pdf
On PA Game Lands you must camp within 200' of the trail. http://www.pacode.com/secure/data/05...5/s135.42.html
In the Cumberland Valley there is no camping at all.