The River City Rascals were a professional baseball team based in O'Fallon, Missouri, in the United States. The Rascals were a member of the West Division of the Frontier League, which is not affiliated with Major League Baseball. From the 1999 season to 2019, the Rascals played their home games at CarShield Field.

O'Fallon is a city in St. Charles County, Missouri, United States. It is part of the St. Louis metropolitan statistical area, located 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 the most populous suburb of St. Louis, 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.