7 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Milan | 1 | 1,714 | 1,818 | -0.98% | 967 | 2 | City |
| Green City | 2 | 557 | 595 | -1.07% | 389 | 1 | City |
| Green Castle | 3 | 204 | 219 | -0.97% | 456 | 0 | City |
| Newtown | 4 | 107 | 115 | -0.93% | 423 | 0 | Town |
| Humphreys | 5 | 86 | 91 | -1.15% | 345 | 0 | Village |
| Harris | 6 | 58 | 61 | 0% | 377 | 0 | Town |
| Pollock | 7 | 43 | 46 | 0% | 259 | 0 | Village |
Milan is the largest city in Sullivan County, with a population of 1,714.
Pollock is the smallest city in Sullivan County, with a population of 43.
There are 7 cities in Sullivan County, Missouri.