| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Marietta | 1 | 12,990 | 13,356 | -0.48% | 1,541 | 8 | City |
| Belpre | 2 | 6,647 | 6,715 | -0.15% | 1,907 | 3 | City |
| Beverly | 3 | 1,193 | 1,234 | -0.58% | 1,749 | 1 | Village |
| Lowell | 4 | 548 | 564 | -0.72% | 2,404 | 0 | Village |
| Macksburg | 5 | 113 | 117 | -0.88% | 523 | 0 | Village |
| Lower Salem | 6 | 71 | 74 | -1.39% | 1,203 | 0 | Village |
| Graysville | 7 | 65 | 68 | -1.52% | 65 | 1 | Village |
Marietta is the largest city in Washington County, with a population of 12,990.
Graysville is the smallest city in Washington County, with a population of 65.
There are 7 cities in Washington County, Ohio.