O'Fallon, Illinois demographics

O'Fallon, IL demographics: median age 37.8; 52.4% of adults 25+ hold a bachelor’s degree. Age, race, households, languages and education, ACS 2020–2024 with margins of error.

ACS 2020–2024 · O'Fallon city, Illinois · Incorporated city · GEOID 1755249. The survey estimates a population of 32,262 for its five-year window. This is separate from the annual July 2025 population estimate on the city overview.

Median age in O'Fallon is 37.8 years, with a 90% margin of error of 1.5 years. There are 12,816 households (±422). Age and household distributions show how these totals are composed; they do not establish which neighborhood suits a particular person.

Every count and share is an estimate. “±” is a 90% margin of error (MOE); pp means percentage points. Derived shares use the category count divided by the named universe. Aggregated category MOEs and percentage MOEs are approximate. A margin larger than half its estimate is flagged as low precision. Blank source uncertainty is shown as unavailable, never zero.

Age distribution and sex

City, state and U.S. estimates · ACS 2020–2024
Measure / survey universe	City estimate ± MOE	State estimate ± MOE	U.S. estimate ± MOE
Median age Total population · years	37.8 ±1.5	39.0 ±0.1	38.9 ±0.1

Age groups · B01001 · ACS 2020–2024 Total population: 32,262
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
Under 18	8,437 ±687	26.2% ±2.1 pp	21.8%	22.0%
18–34	6,471 ±622	20.1% ±1.9 pp	22.7%	22.8%
35–64	11,972 ±782	37.1% ±2.4 pp	38.5%	38.0%
65 and older	5,382 ±583	16.7% ±1.8 pp	17.0%	17.2%

Sex categories as published by ACS · B01001 · ACS 2020–2024 Total population: 32,262
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
Male	15,978 ±549	49.5% ±1.7 pp	49.4%	49.5%
Female	16,284 ±553	50.5% ±1.7 pp	50.6%	50.5%

The age groups are mutually exclusive and cover the entire population. The sex categories follow this ACS table’s published classification; they are not a survey of gender identity.

Race and Hispanic origin

Race · B02001 · ACS 2020–2024 Total population: 32,262
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
White alone	22,610 ±774	70.1% ±2.4 pp	61.0%	61.0%
Black or African American alone	5,468 ±727	16.9% ±2.3 pp	13.6%	12.2%
American Indian and Alaska Native alone	25 ±37 · low precision	0.1% ±0.1 pp · low precision	0.6%	0.9%
Asian alone	846 ±234	2.6% ±0.7 pp	6.0%	6.0%
Native Hawaiian and Other Pacific Islander alone	0 ±27 · low precision	0.0% ±0.1 pp · low precision	0.0%	0.2%
Some other race alone	524 ±263 · low precision	1.6% ±0.8 pp · low precision	7.9%	7.1%
Two or more races	2,789 ±662	8.6% ±2.1 pp	10.9%	12.6%

Hispanic or Latino origin · B03003 · ACS 2020–2024 Total population: 32,262
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
Not Hispanic or Latino	30,601 ±433	94.9% ±1.3 pp	81.2%	80.7%
Hispanic or Latino	1,661 ±432	5.1% ±1.3 pp	18.8%	19.3%

Hispanic origin and race are separate questions. People of Hispanic or Latino origin may be of any race and appear in both tables. Do not add the Hispanic share to race shares. Race alone and two-or-more-race groups are the mutually exclusive categories of the race table.

Household types, children and living alone

Household types · B11001 · ACS 2020–2024 Households: 12,816
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
Married-couple family	7,186 ±404	56.1% ±2.6 pp	45.3%	46.9%
Other family: male householder, no spouse present	550 ±172	4.3% ±1.3 pp	4.9%	5.1%
Other family: female householder, no spouse present	1,405 ±336	11.0% ±2.6 pp	11.9%	12.2%
Nonfamily: householder living alone	3,180 ±456	24.8% ±3.5 pp	31.2%	28.7%
Nonfamily: householder not living alone	495 ±176	3.9% ±1.4 pp	6.7%	7.0%

Households with children · B11005 · ACS 2020–2024 Households: 12,816
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
Households with people under 18	4,619 ±332	36.0% ±2.3 pp	28.6%	29.5%
Households without people under 18	8,197 ±583	64.0% ±4.0 pp	71.4%	70.5%

Household size · B11016 · ACS 2020–2024 Households: 12,816
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
One-person nonfamily households	3,180 ±456	24.8% ±3.5 pp	31.2%	28.7%
Two-person households	4,620 ±506	36.0% ±3.8 pp	32.3%	33.8%
Three-person households	1,851 ±275	14.4% ±2.1 pp	14.7%	15.3%
Four-person households	2,107 ±267	16.4% ±2.0 pp	12.6%	12.6%
Five-person households	727 ±178	5.7% ±1.4 pp	5.8%	5.9%
Six-person households	255 ±113	2.0% ±0.9 pp	2.1%	2.2%
Seven or more people	76 ±71 · low precision	0.6% ±0.6 pp · low precision	1.3%	1.4%

A family household contains related people under the Census definition. A nonfamily household can contain one person or unrelated people sharing a home. Households with children can also appear in the household-type and size tables, so those tables must not be added together. Household estimates exclude people living in group quarters from the household universe.

Nativity and languages spoken at home

Nativity · B05002 · ACS 2020–2024 Total population: 32,262
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
Native	31,038 ±441	96.2% ±1.3 pp	85.3%	85.9%
Foreign born	1,224 ±428	3.8% ±1.3 pp	14.7%	14.1%

Language spoken at home · C16001 · ACS 2020–2024 Population age 5 and older: 30,072
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
English only	28,523 ±685	94.8% ±1.9 pp	76.0%	77.7%
Spanish	621 ±237	2.1% ±0.8 pp	14.0%	13.6%
French, Haitian, or Cajun	10 ±18 · low precision	0.0% ±0.1 pp · low precision	0.3%	0.7%
German or other West Germanic	25 ±28 · low precision	0.1% ±0.1 pp · low precision	0.3%	0.5%
Russian, Polish, or other Slavic	11 ±17 · low precision	0.0% ±0.1 pp · low precision	2.5%	0.7%
Other Indo-European	128 ±106 · low precision	0.4% ±0.4 pp · low precision	2.6%	2.0%
Korean	103 ±66 · low precision	0.3% ±0.2 pp · low precision	0.3%	0.3%
Chinese, including Mandarin and Cantonese	0 ±27 · low precision	0.0% ±0.1 pp · low precision	0.9%	1.1%
Vietnamese	13 ±16 · low precision	0.0% ±0.1 pp · low precision	0.2%	0.5%
Tagalog, including Filipino	128 ±84 · low precision	0.4% ±0.3 pp · low precision	0.7%	0.6%
Other Asian and Pacific Island	138 ±80 · low precision	0.5% ±0.3 pp · low precision	1.0%	1.1%
Arabic	346 ±353 · low precision	1.2% ±1.2 pp · low precision	0.6%	0.5%
Other and unspecified	26 ±42 · low precision	0.1% ±0.1 pp · low precision	0.6%	0.8%

Foreign born means not a U.S. citizen at birth; it includes naturalized citizens. Language categories describe speech at home among people age five and older. A language other than English at home does not establish that someone cannot speak English. This city page uses the published C16001 summary categories because the more detailed B16001 table does not provide these city records in this release.

Educational attainment

Highest completed education · B15003 · ACS 2020–2024 Population age 25 and older: 21,890
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
Less than high school graduate	519 ±176	2.4% ±0.8 pp	9.5%	10.4%
High school graduate or equivalency	3,687 ±455	16.8% ±2.0 pp	25.1%	26.0%
Some college, no degree	3,871 ±547	17.7% ±2.5 pp	19.2%	19.1%
Associate’s degree	2,344 ±346	10.7% ±1.6 pp	8.3%	8.8%
Bachelor’s degree	6,349 ±547	29.0% ±2.4 pp	22.6%	21.6%
Graduate or professional degree	5,120 ±543	23.4% ±2.4 pp	15.3%	14.1%

The denominator excludes residents under 25. Each person is counted in the highest attainment category they completed. This table does not measure the quality of local schools or the education level of every current student.

Residence one year earlier

Geographic mobility · B07003 · ACS 2020–2024 Population age 1 and older: 31,855
Category	Count ± MOE	Share ± MOE (pp)	Illinois	U.S.
Same house	28,110 ±779	88.2% ±2.4 pp	88.9%	87.7%
Moved within same county	1,701 ±557	5.3% ±1.7 pp	6.4%	6.3%
Moved from a different county in the same state	508 ±300 · low precision	1.6% ±0.9 pp · low precision	2.4%	3.1%
Moved from a different state	991 ±291	3.1% ±0.9 pp	1.6%	2.3%
Moved from abroad	545 ±365 · low precision	1.7% ±1.1 pp · low precision	0.6%	0.6%

These are respondents’ residence patterns one year before their survey response, pooled across the five-year window. They are not a net migration count for 2025. A person can move to a different house within the same city or county; moves within the same county should not automatically be interpreted as new arrivals to the city.

Health insurance, internet access and veterans

4.0% of O'Fallon residents (±1.0 percentage points) had no health insurance coverage when surveyed, compared with 6.9% in Illinois and 8.4% nationally. 94.5% of households subscribe to broadband of any type, including cellular data plans. A subscription is not the same as available service: the FCC National Broadband Map shows providers at a specific address.

City, state and U.S. shares · ACS 2020–2024
Measure	O'Fallon	Illinois	U.S.	Compared with Illinois
People without health insurance Civilian noninstitutionalized population	4.0% ±1.0 pp	6.9%	8.4%	Lower
Households with a broadband subscription Households	94.5% ±1.7 pp	90.8%	91.0%	Higher
Veterans Civilian population age 18 and older	20.2% ±2.1 pp	4.8%	6.2%	Higher

Reading and reusing the estimates

The Census table links above lead to the original detailed tables. Counts, source universes and uncertainty are retained in the source observation download for O'Fallon . Compare these figures with the same survey window; do not compare one city’s five-year estimate with another city’s annual estimate as though they measured the same period. For methods, see uncertainty and denominator calculations.

Read O'Fallon housing and cost context or return to the city profile.