Founded in 1812, Johnson County is one of 102 counties in the state of Illinois. Historically, Johnson County was formed from Randolph County. The city of Vienna is the county seat. With FIPS code of 87, Johnson County has a population of 13,463 and area of 343 square miles (888 km2).
List of all cities in Johnson County, IL alphabetically
| City/Town | Postal Code | Area Code |
| Belknap, IL | 62908 | 618/730 |
| Boles, IL | 62909 | 618/730 |
| Buncombe, IL | 62912 | 618/730 |
| Cypress, IL | 62923 | 618/730 |
| Dixon Springs, IL | 62943 | 618/730 |
| Eagle Point Bay, IL | 62939 | 618/730 |
| Elvira, IL | 62912 | 618/730 |
| Ganntown, IL | 62943 | 618/730 |
| Goreville, IL | 62939 | 618/730 |
| Grantsburg, IL | 62943 | 618/730 |
| Lick Creek, IL | 62912 | 618/730 |
| Mermet, IL | 62908 | 618/730 |
| New Burnside, IL | 62967 | 618/730 |
| New Columbia, IL | 62943 | 618/730 |
| Ozark, IL | 62972 | 618/730 |
| Pulleys Mill, IL | 62939 | 618/730 |
| Reevesville, IL | 62943 | 618/730 |
| Reynoldsburg, IL | 62972 | 618/730 |
| Robbs, IL | 62985 | 618/730 |
| Samoth, IL | 62943 | 618/730 |
| Simpson, IL | 62985 | 618/730 |
| Tunnel Hill, IL | 62972 | 618/730 |
| Vienna, IL | 62995 | 618/730 |
| Wartrace, IL | 62943 | 618/730 |