O'Fallon city, Illinois
Official LSAD Designation: O'Fallon city • Census GEOID: 1755249
• St. Clair County
Demographics & Population Profile
Population and demographics for O'Fallon city.
| Demographic Variable | Estimate / Count | Margin of Error | Period | Source |
|---|---|---|---|---|
| Total Population (2025 PEP Estimate) | 32,656 | — | 2025 | Census |
| Median Age | 37.8 yrs | ±1.5 | 2020-2024 | Census ACS 5-Year 2024 |
| Total Households | 12,816 | ±422 | 2020-2024 | Census ACS 5-Year 2024 |
Source: U.S. Census Bureau (PEP, ACS 5-Year).