Unknown Facts About O'fallon Weather Table of ContentsSee This Report on O'fallon Zip CodeThe 10-Second Trick For O'fallon AddressSome Of O'fallonThe 9-Minute Rule for O'fallon Zip CodeO'Fallon is a city in St. Clair Area, Illinois, which was founded in 1854. O'Fallon's namesake comes from Colonel John O'Fallon, that was a well-off gentleman from