Go on the PA web site for state parks. That should answer all your questions. Although I am originally from that area, I have only looked at Locust Lake SP on the web. Overnight spots in that area are pretty slim. Last trip out that way, we stayed at a small private RV park on Rt 895, just off Rt 309 west of Andreas, if I remember correctly, that place was named Locust Lake also.
Correction: It is Laurel Lake Campground, just west of Snyders which is at the intersection of Routs 309 and 895.