Population in O'Fallon, IL
Population in O'Fallon, IL was 32,656 in 2025, according to the U.S. Census Bureau. That is up 1.5% from 2024. That is the 59th highest of 225 cities in 2025.
Population in O'Fallon, IL, 2020 to 2025
All 6 values
| Period | persons |
|---|---|
| 2025 | 32,656 |
| 2024 | 32,186 |
| 2023 | 32,179 |
| 2022 | 32,241 |
| 2021 | 32,395 |
| 2020 | 32,410 |
Compared with Illinois and United States
| Place | 2025 |
|---|---|
| O'Fallon, IL | 32,656 |
| Illinois | 12,719,141 |
| United States | 341,784,857 |
Rankings
Definition
Resident population. Spain and the EU: 1 January, with Spanish figures from the official municipal register (Padrón). Norway: Statistics Norway, 1 January. United States: Census Bureau population estimates for 1 July. United Kingdom regions and local authorities: Office for National Statistics estimates for 30 June. Other countries and the World: World Bank mid-year estimates, which count all residents regardless of legal status or citizenship.
The World Bank series exists for every country, so use it (through compare) to rank countries on one basis.
How to cite
U.S. Census Bureau. Annual estimates of the resident population for incorporated places, 1 July (Population Estimates Program, subcounty totals). https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/. Retrieved 2026-10-12.Citation styles
APA 7
U.S. Census Bureau. (2026). Annual estimates of the resident population for incorporated places, 1 July (Population Estimates Program, subcounty totals) (Population, O'Fallon, IL, 2020 to 2025) [Data set]. Retrieved October 12, 2026, from https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/
MLA 9
Annual estimates of the resident population for incorporated places, 1 July (Population Estimates Program, subcounty totals), Population, O'Fallon, IL, 2020 to 2025. U.S. Census Bureau, 14 May 2026, https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/. Invokely, https://invokely.ai/en/population/ofallon-il. Accessed 12 Oct. 2026.
Chicago (author-date)
U.S. Census Bureau. 2026. Annual estimates of the resident population for incorporated places, 1 July (Population Estimates Program, subcounty totals). Population, O'Fallon, IL, 2020 to 2025. Dataset. Accessed October 12, 2026. https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/. Also distributed by Invokely, https://invokely.ai/en/population/ofallon-il.
Harvard
U.S. Census Bureau (2026) Annual estimates of the resident population for incorporated places, 1 July (Population Estimates Program, subcounty totals), Population, O'Fallon, IL, 2020 to 2025 [Dataset]. Available at: https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/, via Invokely: https://invokely.ai/en/population/ofallon-il (Accessed: 12 October 2026).
BibTeX
@misc{census_population_o_fallon_il_2025,
author = {{U.S. Census Bureau}},
title = {{Annual estimates of the resident population for incorporated places, 1 July (Population Estimates Program, subcounty totals): Population, O'Fallon, IL, 2020 to 2025}},
year = {2026},
howpublished = {Data set},
url = {https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/},
urldate = {2026-10-12},
note = {Accessed via Invokely, https://invokely.ai/en/population/ofallon-il. Publisher attribution: U.S. Census Bureau. Annual estimates of the resident population for incorporated places, 1 July (Population Estimates Program, subcounty totals). https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/. Retrieved 2026-10-12.},
}
RIS
TY - DATA
AU - U.S. Census Bureau
TI - Annual estimates of the resident population for incorporated places, 1 July (Population Estimates Program, subcounty totals): Population, O'Fallon, IL, 2020 to 2025
PY - 2026
DA - 2026/05/14
PB - U.S. Census Bureau
DB - Invokely
UR - https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/
L2 - https://invokely.ai/en/population/ofallon-il
Y2 - 2026/10/12
N1 - Accessed via Invokely, https://invokely.ai/en/population/ofallon-il.
N1 - Publisher attribution: U.S. Census Bureau. Annual estimates of the resident population for incorporated places, 1 July (Population Estimates Program, subcounty totals). https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/. Retrieved 2026-10-12.
ER -
Use this data in your AI agent
Invokely serves this figure to AI assistants through MCP and to code through a REST API, with the source and citation attached. Ask your assistant:
What is the latest population in O'Fallon, IL? Cite the source.
get_value {"indicator":"population","place":"us-place-1755249"}
GET https://invokely.ai/api/v1/value?indicator=population&place=us-place-1755249Questions
What is the population in O'Fallon, IL?
Population in O'Fallon, IL was 32,656 in 2025, according to the U.S. Census Bureau. That is up 1.5% from 2024. That is the 59th highest of 225 cities in 2025.
Where does this figure come from?
U.S. Census Bureau. Annual estimates of the resident population for incorporated places, 1 July (Population Estimates Program, subcounty totals). Retrieved by Invokely on 2026-10-12.
What was the highest population in O'Fallon, IL?
32,656 in 2025, the highest value since 2020 in this series.