Bakers Hole in West Yellowstone. First-come, first-served only; some sites with electricity.
Also, there are a few NFS CGs in the Island Park, Idaho area (near West Yellowstone) with electric sites. Reservations accepted for some of them.
Much farther east, some COE CGs in Iowa and Illinois have electricity at some of their sites, and accept reservations. The ones I'm thinking of are in/near Coralville IA and western Illinois (Thomson, etc., along the Mississippi.)
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