19 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Tarkio | 1 | 1,458 | 1,514 | -0.82% | 1,051 | 1 | City |
| Tarkio | 2 | 1,458 | 1,515 | -0.82% | 1,051 | 1 | City |
| Rock Port | 3 | 1,228 | 1,274 | -0.81% | 443 | 3 | City |
| Rock Port | 4 | 1,228 | 1,275 | -0.81% | 443 | 3 | City |
| Fairfax | 5 | 617 | 646 | -0.96% | 1,327 | 0 | City |
| Fairfax | 6 | 617 | 647 | -0.96% | 1,327 | 0 | City |
| Westboro | 7 | 111 | 115 | -0.89% | 439 | 0 | City |
| Westboro | 8 | 111 | 115 | -0.89% | 439 | 0 | City |
| Big Lake | 9 | 72 | 71 | 0% | 44 | 2 | Village |
| Big Lake | 10 | 72 | 70 | 0% | 44 | 2 | Village |
| Watson | 11 | 55 | 57 | -1.79% | 505 | 0 | Village |
| Watson | 12 | 55 | 57 | -1.79% | 505 | 0 | Village |
| Fortescue | 13 | 21 | 21 | 0% | 273 | 0 | Town |
| Fortescue | 14 | 21 | 21 | 0% | 273 | 0 | Town |
| Quitman | 15 | 19 | 10 | 5.56% | 121 | 0 | CDP |
| Bigelow | 16 | 6 | 6 | 0% | 63 | 0 | Village |
| Bigelow | 17 | 6 | 6 | 0% | 63 | 0 | Village |
| Corning | 18 | 0 | 0 | 0.00 | 0 | Town | |
| Corning | 19 | 0 | 0 | 0.00 | 0 | Town |
Tarkio is the largest city in Atchison County, with a population of 1,458.
Corning is the smallest city in Atchison County, with a population of 0.
There are 19 cities in Atchison County, Missouri.