The Facts About O'fallon Zip Code Revealed Table of ContentsO'fallon Address Things To Know Before You BuyThe 5-Second Trick For O'fallon IlAbout O'fallon IlThe Basic Principles Of O'fallon Attraction O'Fallon is a city in St. Clair County, Illinois, which was established in 1854. O'Fallon's name originates from Colonel John O'Fallon, who was a ri