O'fallon Location Can Be Fun For Everyone Table of ContentsAll About O'fallon AddressSee This Report about O'fallon HourGet This Report about O'fallon MapO'fallon Location - QuestionsO'Fallon is a city in St. Clair County, Illinois, which was founded in 1854. O'Fallon's namesake comes from Colonel John O'Fallon, that was a well-off gent from St. L