We spent several nights at Mauthe Lake campground in the Kettle Moraine State Forest, Wisconsin. It's near Campbellsport, Wisconsin. It's a nicely wooded campground on a lake with one modern bath house but mostly pit toilets. (This seemed to be a theme in the Wisconsin state parks...new bathrooms are being added). Sites are gravel but little leveling was required for the one we chose. Electric sites are available but you have to haul water. Most of the sites are screened by abundant vegetation from the neighbors and the campground is very shady.
This park is located in the beautiful and picturesque dairylands and the state forest preserves many interesting features produced by ice age glaciers. The area is very good for birding and reasonably central to several spots we wanted to visit such as Horicon Marsh, Sheboygan, etc.
Something I missed when researching this trip was that Wisconsin state parks require a $10 daily entry fee on top of the camping fee. However, you can buy a yearly pass for $40 and since we were staying in the state two weeks, that made it more bearable.
I would stay here again anytime.
http://www.dnr.state.wi.us/org/land/parks/specific/kmn/