Custer State Park is a first class state park, on a par with national parks re scenery and wildlife.
You need to get reservations as early as you can. as stated, you have to go through the reservation system anyway.
If you try to wing it, you might get lucky if it is a time with nothing special going on, like 4th July, Sturgis bike rally, 2nd week of August, Buffalo Roundup in the park, last week of Sept.
But there are lots of rv parks in the area, so you can probly get away with dropping in if it isn't one of those extra busy times.
