The Exxon station on Orleans Rd is a long time standard for campers and sits on the border of the park. I have to call out the review here that says there are no places to eat within 50 miles. There's a 100-yard gun range on the north side of the forest that's open six days a week - closed on Tuesdays for maintenance.
There are plenty of hiking trails of varying levels and a boat ramp for access to the Potomac River. It's open year-round which is a big plus for people like me who actually prefer cold weather camping. Also unlike the State Parks, there are no reservation fees for anything but the group sites, so it's only $10 a night for first-come-first served sites. There are just under 100 sites available, spread out over 49,000 acres which, unlike the State Parks, won't leave you camping within earshot of your neighbors.
But, at least for me, that's the worst of it all. The ORV trail has been closed, presumably because of the popularity growth and the resultant damage that couldn't be remedied. In that time, I've seen it's popularity grow to the point where it can be hard to get a site, especially on holiday weekends and when the various hunting seasons are open. Coming from Baltimore, Green Ridge has been my escape from the city for almost 50 years.
