| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Washington | 1 | 7,236 | 7,348 | -0.34% | 1,339 | 5 | City |
| Kalona | 2 | 2,841 | 2,642 | 1.07% | 1,318 | 2 | City |
| Wellman | 3 | 1,544 | 1,521 | 0.32% | 1,440 | 1 | City |
| Riverside | 4 | 1,087 | 1,068 | 0.09% | 589 | 2 | City |
| Brighton | 5 | 586 | 599 | -0.51% | 749 | 1 | City |
| Ainsworth | 6 | 512 | 509 | 0% | 1,388 | 0 | City |
| Crawfordsville | 7 | 278 | 277 | 0% | 757 | 0 | City |
| West Chester | 8 | 147 | 145 | 0% | 581 | 0 | City |
Washington is the largest city in Washington County, with a population of 7,236.
West Chester is the smallest city in Washington County, with a population of 147.
There are 8 cities in Washington County, Iowa.