7 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 |
| Beverly | 3 | 1,198 | 1,231 | -0.42% | 1,757 | 1 | Village |
| Lowell | 4 | 540 | 564 | -0.74% | 2,368 | 0 | Village |
| Macksburg | 5 | 111 | 116 | -0.89% | 514 | 0 | Village |
| Lower Salem | 6 | 68 | 74 | -1.45% | 1,153 | 0 | Village |
| Graysville | 7 | 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 7 cities in Washington County, Ohio.