Ballwin is a western suburb of St. Louis, located in St. Louis County, Missouri, United States. The population was 31,103 as of the 2020 c…Ballwin is a western suburb of St. Louis, located in St. Louis County, Missouri, United States. The population was 31,103 as of the 2020 census. Ballwin was established in 1837. The community was named for John Ball, who settled at the town site in 1804. A post office called Ballwin has been in operation since 1866.