Tricky question, Macca. There were many circuits on USA but not all under the “US GP” name. Well, there were nine F1 circuits in the US: Sebring, Riverside, Watkins Glen, Long Beach, Fair Park, Detroit, Ceasars Pallace, Phoenix and Indianapolis.
But the name “United States Grand Prix” were used by Sebring, Riverside, Watkins Glen, Phoenix and Indianapolis.