11 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Washington | 1 | 1,078 | 1,069 | 0.19% | 1,109 | 1 | City |
| Hanover | 2 | 698 | 692 | 0.14% | 1,165 | 1 | City |
| Clifton | 3 | 458 | 452 | 0.22% | 1,123 | 0 | City |
| Linn | 4 | 390 | 387 | 0.26% | 1,150 | 0 | City |
| Greenleaf | 5 | 352 | 349 | 0.28% | 779 | 0 | City |
| Barnes | 6 | 163 | 163 | 0% | 959 | 0 | City |
| Palmer | 7 | 127 | 124 | 0.79% | 411 | 0 | City |
| Morrowville | 8 | 116 | 116 | 0% | 811 | 0 | City |
| Haddam | 9 | 108 | 108 | 0% | 315 | 0 | City |
| Mahaska | 10 | 44 | 44 | 0% | 197 | 0 | City |
| Hollenberg | 11 | 12 | 12 | 0% | 164 | 0 | City |
Washington is the largest city in Washington County, with a population of 1,078.
Hollenberg is the smallest city in Washington County, with a population of 12.
There are 11 cities in Washington County, Kansas.