Giant City SP, Illinois

Nice campground. Level. Lots of shade. Electric sites. The DNR website shows water hook ups at some sites. If so they've added them over the last few years and I haven't noticed. Use to they had community water faucets around the campground you could fill from.
Giant City SP
It's a very popular state park. I'd recommend getting reservations as soon as you finalize your dates.

Check that you are not going during a cicada hatch. They are deafening. But it's a very nice park.

Just FYI, you might also try Crab Orchard Campground. It is right on the Lake. If I recall, they open Apr 1. Water and electric, but have a dump station. It's a very nice park close to Giant City SP. We stayed there and felt it was a good location, right off Hwy 13 into Carbondale. Cash/check only when we were there.

I can't tell you anything about the campgrounds, but when we used to live down there (near Anna, IL) we used to go to the Sunday dinners at the lodge. They were the best dining experience we've had at a state park. Family style, sit at tables with other families, fried chicken, mashed potatoes, corn, the works. A great experience. That was 20 years ago, but hopefully they've kept that tradition alive.

Never camped there, but wet to college in Carbondale and spent a lot of time at the park. It's beautiful with great hiking trails. There's also several wineries nearby that are worth a stop (if that's your thing).

Also, I agree that giant city lodge is the best Sunday lunch around.