8 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Vienna | 1 | 1,341 | 1,346 | -0.07% | 473 | 2.84 | City |
| Goreville | 2 | 1,058 | 1,063 | -0.09% | 394 | 2.69 | Village |
| Vienna township | 3 | 675 | 660 | 0.45% | 19 | 35.69 | Township |
| Cypress | 4 | 218 | 218 | 0% | 290 | 0.75 | Village |
| Buncombe | 5 | 206 | 206 | 0% | 174 | 1.19 | Village |
| New Burnside | 6 | 153 | 153 | 0% | 146 | 1.04 | Village |
| Belknap | 7 | 85 | 85 | 0% | 80 | 1.06 | Village |
| Simpson | 8 | 44 | 44 | 0% | 84 | 0.53 | Village |
Vienna is the largest city in Johnson County, with a population of 1,341.
Simpson is the smallest city in Johnson County.
There are 8 cities in Johnson County, Illinois.