8 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Washington | 1 | 7,264 | 7,348 | -0.23% | 1,344 | 5 | City |
| Kalona | 2 | 2,792 | 2,642 | 1.09% | 1,296 | 2 | City |
| Wellman | 3 | 1,532 | 1,524 | 0.07% | 1,429 | 1 | City |
| Riverside | 4 | 1,065 | 1,055 | 0.19% | 577 | 2 | City |
| Brighton | 5 | 590 | 600 | -0.34% | 754 | 1 | City |
| Ainsworth | 6 | 511 | 508 | 0% | 1,385 | 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 7,264.
West Chester is the smallest city in Washington County, with a population of 147.
There are 8 cities in Washington County, Iowa.