In Northwestern South Dakota: 12 miles south of Lemmon off SD Hwy 73.
One of the nicest state campgrounds I have been to. The campsites were nice and open and the dump station was really nice.
Beautiful! Be careful picking your site. Use Google earth to find a spot with shade. Some areas closer to the water don't have shade. No service, but isn't that the point if camping? There are a few spots of service and a phone at the check in station if you need to make a call.