O'fallon Weather - An OverviewTable of ContentsThe Ultimate Guide To O'fallon HourThe Buzz on O'fallonGetting My O'fallon Map To WorkLittle Known Facts About O'fallon Location.O'Fallon is a city in St. Clair Region, Illinois, which was started in 1854. O'Fallon's name comes from Colonel John O'Fallon, who was a wealthy gentleman from St. Louis. Thi