
O'Fallon township
- County:
- St. Clair County
- County Seat:
- No
- Area (mi²):
- 35.11
- State:
- Illinois
O'Fallon township is located in St. Clair County, Illinois. O'Fallon township has a 2025 population of 25,805. O'Fallon township is currently declining at a rate of -0.43% annually and its population has decreased by -2.14% since the most recent census, which recorded a population of 26,370 in 2020.
The average household income in O'Fallon township is $123,124 with a poverty rate of 5.75%. The median age in O'Fallon township is 38.3 years: 38 years for males, and 38.7 years for females.