O’Fallon /oʊˈfælən/ 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.^[7] O’Fallon’s namesake in 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.

O’Fallon was founded in 1856 by Nicholas Krekel.^[8] The community was named after John O’Fallon, the president of the North Missouri Railroad.^[9] A post office called O’Fallon has been in operation since 1859.^[10] The St. Mary’s Institute of O’Fallon was listed on the National Register of Historic Places in 2007.^[11]

In 2006, Money Magazine named O’Fallon 39th in its “Best 100 Places to Live.”^[12] Money Magazine also ranked O’Fallon 68th out of 100 in 2008,^[13] 26th out of 100 in 2010,^[14] and 42nd out of 100 in 2017.<sup>[15]

Mastercard has a major presence in O’Fallon. Venture Stores[18]</sup> was headquartered and maintained a distribution center in O’Fallon, until its dissolution. The buildings are now occupied by True Manufacturing. Shell Oil Company announced on February 27, 2012 it will close its regional distribution center here by the end of 2012, costing more than a dozen jobs.[19] Lou Fusz Automotive Dealership in O’Fallon, won the 2012 State of Missouri Bid Contract for Police vehicles for the second year in a row.^[20]

O’Fallon is the home of the River City Rascals independent Frontier League baseball team. The Rascals play at CarShield Field in O’Fallon, which was built in 1999. It is located on Tom Ginnever Boulevard and T.R. Hughes Boulevard near downtown.