Ballwin
- County:
- St. Louis County
- County Seat:
- No
- Area (mi²):
- 8.981
- State:
- Missouri
Ballwin is a city located in St. Louis County, Missouri. Ballwin has a 2026 population of 31,036. Ballwin is currently declining at a rate of 0% annually and its population has decreased by -1.99% since the most recent census, which recorded a population of 31,665 in 2020.