Hontoon Island State Park
This is really getting away from it all. The only way to reach the island is via the ferry (free, and runs all day) or bring your own boat. There are boat docking facilities. This is very primitive camping, $18 per night for tent. You must pack everything in from the ferry or your boat.. There are some very basic cabins available, they book up far in advance. Restrooms and showers are adequate and pretty clean. The trails are good some are very wet at certain times of the year. More than 1600 acres to explore. Its a terrific day half day paddle around the island via kayak too. Mosquitos are thick, bring bug spray! Watch for snakes. There is a nice playground for the kids and a great pavilion for picnicking. You can fish too. No admission charge to come over to the island to just explore for the day if you aren't camping.