8 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Potosi | 1 | 2,547 | 2,555 | -0.08% | 1,094 | 2 | City |
| Potosi | 2 | 2,547 | 2,555 | -0.08% | 1,094 | 2 | City |
| Irondale | 3 | 368 | 367 | 0% | 690 | 1 | City |
| Irondale | 4 | 368 | 367 | 0% | 690 | 1 | City |
| Mineral Point | 5 | 236 | 226 | 0.85% | 983 | 0 | Town |
| Mineral Point | 6 | 236 | 226 | 0.85% | 983 | 0 | Town |
| Caledonia | 7 | 132 | 132 | 0% | 805 | 0 | Village |
| Caledonia | 8 | 132 | 132 | 0% | 805 | 0 | Village |
Potosi is the largest city in Washington County, with a population of 2,547.
Caledonia is the smallest city in Washington County, with a population of 132.
There are 8 cities in Washington County, Missouri.