O'Fallon, Missouri

O'Fallon population, 2020 to 2024

O'Fallon added 3,690 residents from July 2020 to July 2024, a change of +4.0%. In the latest year it moved by +937. Among 135 Missouri places of 5,000 or more, that growth ranks 42nd; the median place changed by +1.2%. The median place of 5,000+ in Missouri has 12,239 people, so O'Fallon is 7.8 times that size.

O'Fallon covers 30.55 square miles of land, for 3,121 people per square mile of land. The median Missouri place of 5,000+ has 1,448, so O'Fallon is denser than the typical town.

What county O'Fallon is in

All of O'Fallon's residents live in St. Charles County, which had 423,726 residents in 2024. O'Fallon holds 22.5% of the county's population. The shaded shape is on the map above; dots mark the eight nearest places.

ZIP codes in O'Fallon

3 ZIP Code Tabulation Areas (ZCTAs) overlap O'Fallon by at least 10% of the ZCTA's or the city's land: 63366, 63367, 63368. 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 38.784700, -90.720700. Jefferson City, the capital, is 79.6 miles W in a straight line. The nearest larger place is St. Louis, MO (279,695 people), 27.7 miles away.

Daylight in O'Fallon

At 38.78° N, O'Fallon gets about 14 h 53 min of daylight around the June solstice and 9 h 27 min around the December solstice, a swing of 5 h 26 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 Missouri, measured between internal points. The closest is Dardenne Prairie, 3.0 miles away, with 14,407 people.