11 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Montana City | 1 | 2,716 | 2,821 | 0% | 80 | 34 | CDP |
| Clancy | 2 | 2,047 | 1,964 | 1.24% | 52 | 39 | CDP |
| Boulder | 3 | 1,330 | 1,200 | 1.92% | 1,183 | 1 | City |
| Boulder | 4 | 1,330 | 1,205 | 1.92% | 1,183 | 1 | City |
| Whitehall | 5 | 1,143 | 1,003 | 2.42% | 1,621 | 1 | Town |
| Whitehall | 6 | 1,143 | 1,008 | 2.42% | 1,621 | 1 | Town |
| South Hills | 7 | 657 | 586 | 1.39% | 112 | 6 | CDP |
| Jefferson City | 8 | 482 | 596 | 0.21% | 21 | 23 | CDP |
| Rader Creek | 9 | 411 | 295 | 0.98% | 20 | 20 | CDP |
| Basin | 10 | 402 | 267 | 3.34% | 32 | 13 | CDP |
| Cardwell | 11 | 60 | 107 | 7.14% | 28 | 2 | CDP |
Montana City is the largest city in Jefferson County, with a population of 2,716.
Cardwell is the smallest city in Jefferson County, with a population of 60.
There are 11 cities in Jefferson County, Montana.