There's a little...
Wakeeny, KS has a KOA campground. It's about 90 minutes away. Oakley, KS has another commercial campground that is about an hour away.
Cedar Bluff State Park would probably be the best and closest actual camping experience. I camped there last summer and it's a nice place for Western Kansas, but it's about two hours away. However, as my friend Ex-Coloradan has pointed out, Castle Rock is close by, and is in between Cedar Bluff and Castle Rock. Here's a screen shot of Google Maps to kind of show it the area. This is not necessarily the route I would take.
I don't know why it shows up so small, but A is Cedar Bluff, B is Castle Rock, and C is Monument Rocks. (You're looking at Western Kansas, with the Nebraska and Colorado borders shown.)
Edit: Another option is Scott State Park. Its about an hour away and has camping.
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Here is a picture of Castle Rock, not too far away from Monument Rocks is it TripLeader?
This is from a visit we made a couple of years ago to Castle Rock. One of these days I'll try to add some of my Castle Rock photos.