| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Potosi | 1 | 2,567 | 2,556 | -0.04% | 1,103 | 2 | City |
| Irondale | 2 | 371 | 367 | 0% | 696 | 1 | City |
| Mineral Point | 3 | 236 | 226 | 0.43% | 983 | 0 | Town |
| Caledonia | 4 | 134 | 132 | 0% | 817 | 0 | Village |
Potosi is the largest city in Washington County, with a population of 2,567.
Caledonia is the smallest city in Washington County, with a population of 134.
There are 4 cities in Washington County, Missouri.