| City : | O'fallon City |
| County : | St. Clair County |
| State : | Illinois (IL) |
| | |
| Land Area : | 14.35 sq mi |
| Water Area : | 0.12 sq mi |
| Latitude : | 38.5943436 |
| Longitude : | -89.9150420 |
| | |
| Population (2010): | 28,281 |
| Population Estimate (2012) : | 28,377 |
| Population Density : | 1,970.25/sq mi |
| Housing Units (2012) : | 11,414 |
| Median Household Income (2012) : | $76,268 (Illinois : $56,853, USA : $53,046) |
| Median Family Income (2012) : | $90,347 (Illinois : $70,144, USA : $64,585) |
| Median House Price (2012) : | $199,900 (Illinois : $190,800, USA : $181,400) |