O'Fallon, Illinois

O'Fallon population, 2020 to 2024

O'Fallon lost 244 residents from July 2020 to July 2024, a change of -0.8%. In the latest year it moved by -17. Among 330 Illinois places of 5,000 or more, that growth ranks 158th; the median place changed by -0.9%. The median place of 5,000+ in Illinois has 14,760 people, so O'Fallon is 2.2 times that size.

O'Fallon covers 15.81 square miles of land and 0.11 of water, for 2,035 people per square mile of land. The median Illinois place of 5,000+ has 2,177, so O'Fallon is close to the typical town.

What county O'Fallon is in

All of O'Fallon's residents live in St. Clair County, which had 251,149 residents in 2024. O'Fallon holds 12.8% of the county's population. The shaded shape is on the map above; dots mark the eight nearest places.

ZIP codes in O'Fallon

1 ZIP Code Tabulation Area (ZCTA) overlaps O'Fallon by at least 10% of the ZCTA's or the city's land: 62269. ZCTAs are Census approximations of USPS ZIP code delivery areas. The list comes from the 2020 ZCTA to place relationship file, so a city that annexed land after 2020 may reach into ZIP codes not listed here.

Where O'Fallon is

The Census internal point of O'Fallon is at 38.600000, -89.915400. Springfield, the capital, is 82.8 miles N in a straight line. The nearest larger place is Belleville, IL (40,560 people), 7.1 miles away. The nearest city of 100,000 or more is St. Louis, MO, 18.0 miles away.

Daylight in O'Fallon

At 38.60° N, O'Fallon gets about 14 h 52 min of daylight around the June solstice and 9 h 28 min around the December solstice, a swing of 5 h 24 min. Figures are sunrise to sunset from the SunCalc model for June 21 and December 21, 2026.

Places near O'Fallon

The eight nearest incorporated places of 1,000+ in Illinois, measured between internal points. The closest is Shiloh, 3.5 miles away, with 14,754 people.