There are a couple campgrounds within very close proximity of
Indiana Beach (Monticello, Indiana), they even offer shuttle service to the park or you can walk.
The other one we've been to is Lake Fairfax Park (Fairfax County, Virginia ... Reston, Virginia).
Click here. There is a water park right there at the park. It's not anything as large as 6 Flags or anything, but it's a nice park.
Not in the campground, but Santa Clause, Indiana has
Holiday World and Splashin' Safari. VERY close by campgrounds include Lincoln State Park, and Camp Rudolph. There are several more in the area too.
