Canyon Campground, Gallatin National Forest

This campground is in Gallatin National Forest, and has 17 first come first serve sites. Huge boulders separate many of the sites, making it feel unique and private. The campground is right off the highway, so expect some road noise, but the boulders do help with this as well. Yellowstone River flows on the opposite side of the highway. Canyon Campground doesn't have any water, but does have vault toilets and picnic tables.
The campground is located just north of Gardiner. Yellowstone National Park also has a 'Canyon Campground' about 50 miles southeast, so make sure you're heading to the right one!