We visited once as a day trip from our campsite, which I believe was at Wyalusing SP in Wisconsin - basically just across the river. Neat little park, and I'd recommend it.
Other CGs in that area besides Wyalusing (which you need to spend time at, plus not a lot of pull-in, pull-out sites; it's quite popular) that we have camped at include Spruce Creek Park in Bellevue, a county park. Nothing special, can be full on weekends (no reservations taken). Also Rustic Barn RV Park in Kieler, Wisconsin. Nice little place - we quite liked it.
Our visit to Effigy Mounds was long enough ago that I don't remember the parking lot. Sorry can't provide info on that.