Is it walk-in, or online reservations?
Most of the state parks here in Michigan sell out for holidays and summer weekends between Thanksgiving and New Years. It's sad because so many abuse the res system. They'll reserve at multiple parks and then cancel last minute, ruining it for other campers and cheating the park out of much needed revenue.
I like that I can make reservations, but feel there should be a no-refund policy. If I'm having an emergency and can't make it, $100 lost on a campground isn't be a big concern.