Missouri, United States·92K residents
O'Fallon is a city in St. Charles County, Missouri, United States. It is part of the St. Louis metropolitan statistical area, along Interstates 64 and 70 between Lake St. Louis and St. Peters. As of the 2020 census, O'Fallon had a population of 91,316, making it St. Louis's most populous suburb as well as the most populous municipality in St. Charles County and the 7th-most populous in Missouri. O'Fallon's namesake in St. Clair County, Illinois, is also part of the St. Louis region. The two cities are one of the few pairs of same-named municipalities to be part of the same metro area.
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