O'Fallon is a city along Interstate 64 and Interstate 70 between Lake St. Louis and St. Peters in St. Charles County, Missouri, United States. It is part of the St. Louis Metropolitan Statistical Area. As of the 2010 census O'Fallon had a population of 79,329, making it the largest municipality in St. Charles County and seventh largest in the state of Missouri. O'Fallon's namesakein St. Clair County, Illinois is also part of the St. Louis Metropolitan Statistical Area. The two O'Fallons are one of the few pairs of same-named municipalities to be part of the same MSA.
Information From Third Parties, Deemed Reliable But Not Verified.