Convenient Camping for Rushmore, Crazy Horse & Custer State Park
If you're touring the Black Hills, and hitting all of the outdoor attractions, Horsethief Lake is perfectly placed to access it all. The sites are basic, but have everything you need -- toilets, firepit, picnic table.
We were traveling with a small trailer and a tent, and there wasn't much room to fit them both on the same site, and had the choice to either pitch the tent on gravel, or on a slope (site #20). There were lots of trees that worked to hang up the hammock which was a positive. There weren't many available sites to choose from due to the proximity of the campground to Rushmore.
This campground is one of the closest (if not THE closest to Rushmore), and allows you close access to the park without having to stay in the touristy trap town of Keystone. There isn't any cell access in the campground, but you can drive up to Rushmore for a very clear signal if needed.
If you're spending a lot of time in the Black Hills, there are plenty of National Forest and state park campgrounds to choose from. This one is mostly great as a peaceful place to camp if you're intending to see the area.