Warren County, Illinois
County seat: Monmouth · Population 16,222 (2025) · 542 sq mi
Warren County is the 65th most populous of Illinois's 102 counties, with 16,222 people (2025 estimate). Its county seat is Monmouth. It is part of the West Central region, one of the 10 Illinois economic development regions (DCEO). The map shows its 6 cities and towns and the 5 neighboring counties.
Warren County facts
- County seat
- Monmouth
- Population (2025 estimate)
- 16,222 −3.7% since 2020
- Land area
- 542 sq mi 47th largest of 102
- Water area
- 1 sq mi
- Population density
- 30 per sq mi
- Established
- 1825
- Same name
- One of 14 Warren Counties in the US
- Named after
- Joseph Warren American doctor (1741-1775)
- Largest city
- Monmouth 8,599
- Median household income
- $67,385
- Cities and towns
- 6 plus 1 CDPs
- ZIP codes
- 14
- Time zone
- Central
- FIPS code
- 17187
Cities and towns in Warren County
Warren County has 6 incorporated cities, towns and villages. Populations count the people living inside Warren County; cities that cross a county line also list the other counties.
| Name | Type | Population 2025 | Also in |
|---|---|---|---|
| Monmouth (county seat) | City | 8,599 | |
| Roseville | Village | 843 | |
| Kirkwood | Village | 650 | |
| Alexis | Village | 425 | Mercer County |
| Little York | Village | 267 | |
| Avon | Village | 4 | Fulton County |
Unincorporated communities (CDPs)
Census-designated places are communities without their own city government; the county provides their services.
| Community | Population | Also in |
|---|---|---|
| Cameron | 280 |
ZIP codes in Warren County
14 ZIP codes reach into Warren County. ZIP codes ignore county lines, so some also cover a neighboring county.
- 61401 also Knox County
- 61410 also Knox County
- 61412 also Mercer County
- 61415 also Fulton County
- 61417
- 61423
- 61435
- 61447 also Henderson County
- 61453 also Henderson County
- 61462 also Henderson County
- 61473
- 61474 also Knox and Fulton counties
- 61475 also McDonough and Henderson counties
- 61478 also Henderson County
Population of Warren County, 2020–2025
Warren County shrank by 622 people (−3.7%) between April 2020 and July 2025: 70 more deaths than births and a net loss of 572 people from migration.
| Year (July 1) | Population |
|---|---|
| 2020 | 16,837 |
| 2021 | 16,622 |
| 2022 | 16,278 |
| 2023 | 16,159 |
| 2024 | 16,116 |
| 2025 | 16,222 |
Neighboring counties
- Henderson County west · 5,984 people
- Knox County east · 47,767 people
- McDonough County south · 25,916 people
- Mercer County north · 15,229 people
- Fulton County southeast · 32,901 people
Printable Warren County map
The PDF is a vector file with real text: it prints sharp on Letter paper and you can search it for a town. The PNG is 2400 pixels wide for slides and documents. Both are free to use with a credit to WhichCounty.
- PDF (Letter) (76 KB)
- PNG (2400 px) (67 KB)
Paste this code to embed the map on your site:
Sources
- Boundaries: U.S. Census Bureau, 2025 Cartographic Boundary Files (1:500,000).
- Population: Census Bureau county and city estimates, Vintage 2025. CDP populations: American Community Survey 2020–2024.
- Places and ZIP codes: Census Bureau 2026 Gazetteer and 2020 ZIP Code Tabulation Area relationship files.
- County seat, founding year and name origin: Wikidata (CC0), checked against state sources.
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