O'Fallon Flag

O'Fallon

County Seat:
No
Area (mi²):
15.791
State:
Illinois

O'Fallon is a city located in St. Clair County, Illinois. O'Fallon has a 2026 population of 32,169. O'Fallon is currently declining at a rate of -0.05% annually and its population has decreased by -0.75% since the most recent census, which recorded a population of 32,413 in 2020.

32.2K
Total Population
2,037
Density (mi²)
-17 -0.05%
Growth

Nearby Cities

Sources

  1. US Census State Population Estimates - Most recent state estimates from the Census Bureau's Population Estimates Program
  2. US Census County Population Estimates - Most recent county estimates from the Census Bureau's Population Estimates Program
  3. American Community Survey (2009 - 2013)
  4. Census QuickFacts
  5. Historical Populations of States and Counties (1790 - 1990)