Threemile Campground is a nice campground just three miles from Yellowstone NP.  However this campground is not for tent campers as only hard sided campers are allow due to bears in the area.  The campground has 21 sites, all with picnic tables, metal fire rings and poles to hang your lantern on and bear lockers for food storage.  Vault toilets serve the campground.  Water is available as well as a bear proof dumpster for your trash.  And about those bears, two black bear cubs were seen just a few miles down the highway.   Campsite are nicely spread apart and sit in a mature pine forest.