24 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Marietta | 1 | 12,878 | 13,361 | -0.62% | 1,528 | 8 | City |
| Belpre | 2 | 6,522 | 6,719 | -0.5% | 1,871 | 3 | City |
| Muskingum | 3 | 4,247 | 4,372 | -0.31% | 200 | 21 | Township |
| Marietta | 4 | 4,163 | 4,277 | -0.26% | 281 | 15 | Township |
| Belpre | 5 | 3,791 | 3,909 | -0.34% | 162 | 23 | Township |
| Waterford | 6 | 3,460 | 3,553 | -0.2% | 93 | 37 | Township |
| Barlow | 7 | 2,505 | 2,583 | -0.32% | 79 | 32 | Township |
| Dunham | 8 | 2,495 | 2,555 | -0.2% | 107 | 23 | Township |
| Newport | 9 | 1,867 | 1,927 | -0.37% | 53 | 35 | Township |
| Adams | 10 | 1,481 | 1,537 | -0.54% | 48 | 31 | Township |
| Watertown | 11 | 1,467 | 1,511 | -0.27% | 40 | 36 | Township |
| Grandview | 12 | 1,364 | 1,407 | -0.37% | 39 | 35 | Township |
| Beverly | 13 | 1,198 | 1,231 | -0.42% | 1,757 | 1 | Village |
| Wesley | 14 | 936 | 960 | -0.21% | 30 | 31 | Township |
| Fearing | 15 | 856 | 873 | -0.12% | 37 | 23 | Township |
| Lawrence | 16 | 791 | 811 | -0.25% | 23 | 35 | Township |
| Palmer | 17 | 555 | 564 | -0.18% | 25 | 23 | Township |
| Lowell | 18 | 540 | 564 | -0.74% | 2,368 | 0 | Village |
| Liberty | 19 | 423 | 434 | -0.24% | 14 | 29 | Township |
| Aurelius | 20 | 302 | 305 | 0.33% | 22 | 14 | Township |
| Ludlow | 21 | 257 | 267 | -0.39% | 12 | 22 | Township |
| Macksburg | 22 | 111 | 116 | -0.89% | 514 | 0 | Village |
| Lower Salem | 23 | 68 | 74 | -1.45% | 1,153 | 0 | Village |
| Graysville | 24 | 65 | 68 | 0% | 65 | 1 | Village |
Marietta is the largest city in Washington County, with a population of 12,878.
Graysville is the smallest city in Washington County, with a population of 65.
There are 24 cities in Washington County, Ohio.