We stayed 5 nights and used this as a base camp to visit the Black Hills: it was the best choice. The park is huge and sites are big. The bike trail goes right by, if we had know that we would have brought our bikes. Make reservations as people were turned away daily. We made ours several months in advance. Has a nice camp store with ice cream. The only downside was a huge noisy family reunion right next to us.
This is a great park to stay at on your way through Montana. It is close to Little Big Horn. The park is rocky and on a hill but our site was very level. It is hot here in the summer. They were very friendly, we were given ice cream bars when we registered. The restrooms were about the cleanest I've seen.
We saw this park from I-90 on our way out and decided to try it on our way back home. It is a beautiful setting: right on the river. Old Mission is nearby and a 70 mile bike trail runs right by. The sites were level and open, park is quiet even though by the freeway. Would definitely stay again as the price is right. No credit cards taken.