| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| St. Joseph | 1 | 70,743 | 72,134 | -0.36% | 1,606 | 44 | City |
| Agency | 2 | 647 | 665 | -0.61% | 176 | 4 | Village |
| De Kalb | 3 | 245 | 232 | 0.82% | 961 | 0 | Town |
| Easton | 4 | 226 | 225 | 0% | 384 | 1 | City |
| Rushville | 5 | 220 | 226 | -0.45% | 1,111 | 0 | Village |
| Ridgely | 6 | 104 | 97 | 0.97% | 75 | 1 | Village |
| Lewis and Clark Village | 7 | 91 | 94 | -1.09% | 149 | 1 | Town |
St. Joseph is the largest city in Buchanan County, with a population of 70,743.
Lewis and Clark Village is the smallest city in Buchanan County, with a population of 91.
There are 7 cities in Buchanan County, Missouri.