Founded in 1818, Union County is one of 102 counties in the state of Illinois. Historically, Union County was formed from Johnson County. The city of Jonesboro is the county seat. With FIPS code of 181, Union County has a population of 16,923 and area of 413 square miles (1,070 km2).
List of all cities in Union County, IL alphabetically
| City/Town | Postal Code | Area Code |
| Alto Pass, IL | 62905 | 618/730 |
| Anna, IL | 62906 | 618/730 |
| Balcom, IL | 62906 | 618/730 |
| Cobden, IL | 62920 | 618/730 |
| Dongola, IL | 62926 | 618/730 |
| Jonesboro, IL | 62952 | 618/730 |
| Millcreek, IL | 62961 | 618/730 |
| Reynoldsville, IL | 62952 | 618/730 |
| Saratoga, IL | 62906 | 618/730 |
| Ware, IL | 62952 | 618/730 |
| Wetaug, IL | 62926 | 618/730 |
| Wolf Lake, IL | 62998 | 618/730 |