More About O'fallon Location Table of ContentsThe Best Guide To O'fallon LocationGetting The O'fallon Weather To WorkThe Basic Principles Of O'fallon Map Some Known Questions About O'fallon Address.O'Fallon is a city in St. Clair Region, Illinois, which was started in 1854. O'Fallon's namesake comes from Colonel John O'Fallon, who was a well-off g