What part of Illinois?

There's a nice little park in western Indiana, near the Illinois line just south of Crawfordsville along I74, called Shades State Park. It has a non-electric car campground (no electric = no RVs), and it has a backpack-only campground at the end of a 2-mile trail (pretty plush: an outhouse and a water hydrant.) The scenery is great; you hike from a plateau down to a creek through very pretty ravines, and can adjust the length of your hike as you go to fit how you're feeling. The trails (a total of about 10 miles, plus the 2-mile trail to the backpack camp) all loop you back to a common trailhead, so you can get or leave stuff at your car as needed.

All in all, it's a great place for beginners to hone their skills in a user-friendly yet picturesque setting, or for anyone who needs a shakedown at the start of the season or when they want to experiment with different gear and style. (I'm headed there this weekend for exactly that purpose.)