8 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Milan | 1 | 1,721 | 1,816 | -1.09% | 971 | 1.77 | City |
| Green City | 2 | 564 | 599 | -1.23% | 394 | 1.43 | City |
| Green Castle | 3 | 208 | 218 | -0.95% | 465 | 0.45 | City |
| Newtown | 4 | 105 | 114 | -1.87% | 415 | 0.25 | Town |
| Humphreys | 5 | 86 | 91 | -1.15% | 345 | 0.25 | Village |
| Harris | 6 | 60 | 64 | -1.64% | 390 | 0.15 | Town |
| Pollock | 7 | 45 | 47 | 0% | 271 | 0.17 | Village |
| Winigan | 8 | 10 | 26 | 11.11% | 20 | 0.50 | CDP |
Milan is the largest city in Sullivan County, with a population of 1,721.
Winigan is the smallest city in Sullivan County.
There are 8 cities in Sullivan County, Missouri.