Founded in 1825, Warren County is one of 102 counties in the state of Illinois. Historically, Warren County was formed from Schuyler County. The city of Monmouth is the county seat. With FIPS code of 187, Warren County has a population of 16,531 and area of 542 square miles (1,404 km2).
List of all cities in Warren County, IL alphabetically
| City/Town | Postal Code | Area Code |
| Berwick, IL | 61417 | 309 |
| Cameron, IL | 61423 | 309 |
| Eleanor, IL | 61453 | 309 |
| Ellison, IL | 61478 | 309 |
| Gerlaw, IL | 61435 | 309 |
| Kirkwood, IL | 61447 | 309 |
| Larchland, IL | 61462 | 309 |
| Little York, IL | 61453 | 309 |
| Monmouth, IL | 61462 | 309 |
| Ormonde, IL | 61462 | 309 |
| Roseville, IL | 61473 | 309 |
| Rozetta, IL | 61447 | 309 |
| Smithshire, IL | 61478 | 309 |
| Swan Creek, IL | 61473 | 309 |
| Tompkins, IL | 61447 | 309 |
| Youngstown, IL | 61473 | 309 |