St. Clair
- County:
- Franklin County
- County Seat:
- No
- Area (mi²):
- 4.808
- State:
- Missouri
St. Clair is a city located in Franklin County, Missouri. St. Clair has a 2026 population of 4,748. St. Clair is currently declining at a rate of -0.17% annually and its population has decreased by -1.72% since the most recent census, which recorded a population of 4,831 in 2020.