Coffee Park is a city (well, "village"--Harrison owns it last I knew) park; I don't think camping is allowed. I was up there some years ago, doing some biological survey work for a project. Sometimes in the summer you can trip over the birdwatchers. . . other than the park it is all privately owned. Many of the birdwatchers seem to think the entire valley is part of the park.
It can be kinda fun watching the preserve-nature-hunting-is-evil-tree-huggers when they get up there. Then they trip over a rattlesnake and suddenly want "someone" to kill all the snakes "for the children". It probably didn't help that while I was there, "someone" relocated one of the snakes over the fence and told the idiots that the ranchers stock the snakes so people won't trespass. On the other hand, one old lady from back East asked me to hold the snake so she could key it out: this was the second rattlesnake she'd seen in her life, and she wanted to know the species! (Crotalus viridis for the curious.)
When there isn't a lot of traffic (say, a Tuesday morning before Memorial Day), the Valley makes a great day hike. From one end to the other it is about 12 miles IIRC.