Surprisingly enough there are still campsites available at State Park Campgrounds. Usually the 4th of July holiday sees 100% capacity at nearly every park. It is one of the biggest (along with Labor Day Weekend) camping dates on the summer calendar. You will be most successful in finding a site if you choose one of the lesser known (but still wonderful) Michigan State Parks. The Detroit Free Press has a list of the current occupancy report and you can visit Michigan.gov/dnr for a list that is supposed to be updated each morning.