We've been wanting to explore southern Illinois for a long time, but it's a six hour (min)  drive from our home. Our first choice was Giant City state park, but this was recommended to us as a cozier, more manageable alternative. It's close to Giant City so you can take advantage of the trails there and eat at the magnificent old Lodge. The campground is on little Grassy lake, it has a marina with boat rentals of all types and a free launch. The lake is too small for speedboats, and is great for fishing (there's a hatchery with tours close by), canoeing & kayaking. there's also a beach, separate form the marina that's quite nice and secluded. Sites are big and shady. but open to each other. Our host, a fun lady named Turtle, let us take a double site to give us room to spread out.
Our site had a nice firepit slightly downhill with western view of the lake. We were able to tie up our canoe there too. Water & electric are available most sites, with more 50amp sites to be added soon.
Bathrooms and showers are spacious and clean with good hot water.
There's a general store with the usual camp things and fishing supplies at the marina, though there's a great one 9 miles east at Grassy Rd. & Rt 148 with an amazing selection of local snacks, sodas, beer & liquor.
While we enjoyed staying here, we used it as our base camp for the ten days we were there to visit places as far east as Cave In Rock state park, and south to Paducah KY & Metropolis, and all the places in Shawnee national Forest, like Garden of the Gods and the Cache River Bayou (very different canoeing from anywhere else north of Louisiana).
The nearest town is Makanda, voted "Hippiest town in Illinois" cool shops and funky vibe, but very limited hours & services. like, no gas station.

For an activity that's on the unusual side, we recommend Shawnee Canopy zip-line tours.