Ben Fromme Memorial RV Park, Island Park, Idaho
Great free spot right on Henrys Lake! About 22-24 miles from West Yellowstone and the park. 14 day limit, but no one really keeps careful track even though there is a host, you seldom see him.
About 30 sites, several with good shade. Vault toilet. No hookups, make sure you have water and are ready to pack it in and pack it out. There is a boat ramp and a couple of docks as well, in pretty good shape!
Road is gravel and sites are gravel as well. All is fairly level, was easy to get set up. Most sites have picnic table and burn pits, but not all. All in all, a heck of a deal! I will definitely be back next time I'm in the area. Pretty good Verizon reception, 2-3 bars.
GPS: 44.649733, -111.438296