Hocking Hills State Park closes at dusk. All parking lots are cleared of vehicles at that time so you cannot park there. There are primitive campsites you can rent: https://www.reserveamerica.com/explore/hocking-hills-state-park/OH/960009/campsites?siteTypeId=120&nextAvailableDate=false&availStartDate=2019-07-15&lookingFor=2003&pageNumber=0
Hundreds of them around. You can get a list almost any place. I got one in interstate rest area
The sites close just after sunset. Top O the Caves campground has reasonable prices and is near most of the caves and falls
There is a campground real close and it's not too expensive it's called top of the caves check there
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