I take it that you will be coming from NJ. The simplest route would be to use the Morgantown, PA turnpike exit 298. Take rte 10 (south?) toward Mogantown. Make a left turn onto rte 23 east; I think it is at the 2nd traffic signal after exiting the turnpike. Take rte 23 east through Elverson to rte 345 north (left turn off rte 23). Go about 3 miles (?). Road to the park will be on the left. Be careful, the sign is not very big and you may pass it by.
This route will require you to backtrack a few miles, but trust me, it is the easiest and less congested way to go. I live just outside of Phoenixville and we have taken our grandchildren camping in French Creek many times.
I forgot to tell you to do a search for "French Creek state park". There is additional info there from 2013 including a post I made regarding some of the sites.
Hope you enjoy your stay.
Ray