https://www.nps.gov/badl/planyourvisit/camping.htm
There are 2 campgrounds in the park; 1 with electric and on the paved road and a fee, and Sage Creek which has no hookups, is free with buffalo. it is 13 miles off the paved road. The gravel road can be washboardy. I spent a night there alone and enjoyed it. Vault toilets were clean.