A local DJ asked this trivia question: What is the only town name common to all 50 states? The answer was Greenville (or various spellings thereof). Maybe the masses from around the US can help me verify from their knowledge!
(FYI: One person I met originally from Hawaii claims there could be such a town. Although I WAGed all Hawaii towns are of Hawaiian origin, she explained how the influx of mainland USA business to Hawaii has placed non-Hawaiian town names on the map.)