Great place to go for a day hike or stay for a few days. There are 21 miles of trails throughout the park and a large lake. The attractions are all relatively close to the road (cave, "hidden" spring, and trout streams). The campgrounds are easy to get to and close to a few trails. They have kayak and canoe rentals available for the lake and it appeared to be a great place to fish. It was an enjoyable experience.
Maybe it's because I am from WI and we tend to rip on IL a lot, but I really found this park sub-par. I am also spoiled from getting to see some of the larger parks in the country. Would probably be nice for a long weekend with the kids. But I don't have kids. It's more of a touristy place than a real campground in my opinion. If you are in the area check out the view of Tower Rock. There are a lot of campsites available for both tent and RV, and they do offer grills, tables, camp fire pits, toilets, and a playground. Pets are welcome. Part of a foundation of an old house built on a rock is still around and is a neat part of history.