Red Barn Campground in Shell Lake, WI is a good one if you have kids. They have animals on site and the kids can walk and pet them. Kids can also do horse back rides (very slow rides within the campground), and they can harvest an egg from the chicken coop.
Wildwood campground near Taylors Falls, MN is a decent place to stay and is near Interstate state park with lots of excellent hiking, exploring, and canoe/kayak rental. Also near Wild Mountain which is a water park with alpine sleds and go-karts.
Camp near Duluth, MN and explore that city along with places like Gooseberry Falls, Split Rock Lighthouse and a day trip to Grand Marais.
Check out Itasca State Park and visit the Mississippi head waters, climb their old fire observation tower, and drive/hike through the park. Very pretty!
I've heard good things about the new Minneapolis NE KOA and we're checking that out very soon. It's close to the Twin Cities if you're looking to explore that area.
Weekend availability at MN state parks is hard to come by if you want electricity but weekday availability is easier to find.