19 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Mount Vernon | 1 | 17,462 | 17,063 | 0.39% | 1,760 | 10 | City |
| Howard | 2 | 6,181 | 5,882 | 0.65% | 274 | 23 | Township |
| Hilliar | 3 | 3,879 | 3,787 | 0.1% | 149 | 26 | Township |
| College | 4 | 2,685 | 2,551 | 0.15% | 427 | 6 | Township |
| Fredericktown | 5 | 2,662 | 2,650 | 0.08% | 1,342 | 2 | Village |
| Union | 6 | 2,576 | 2,628 | -0.43% | 86 | 30 | Township |
| Gambier | 7 | 2,397 | 2,219 | 1.27% | 2,558 | 1 | Village |
| Brown | 8 | 2,126 | 2,054 | 0.38% | 71 | 30 | Township |
| Morris | 9 | 2,102 | 2,103 | 0.05% | 101 | 21 | Township |
| Liberty | 10 | 1,997 | 1,927 | 0.45% | 78 | 26 | Township |
| Pleasant | 11 | 1,702 | 1,667 | 0.24% | 95 | 18 | Township |
| Pike | 12 | 1,700 | 1,674 | 0% | 56 | 30 | Township |
| Centerburg | 13 | 1,700 | 1,703 | 0% | 1,758 | 1 | Village |
| Clay | 14 | 1,517 | 1,548 | -0.46% | 60 | 25 | Township |
| Middlebury | 15 | 1,436 | 1,397 | 0.14% | 70 | 21 | Township |
| Morgan | 16 | 1,112 | 1,066 | 0.63% | 43 | 26 | Township |
| Miller | 17 | 1,084 | 1,058 | 0.46% | 52 | 21 | Township |
| Danville | 18 | 1,000 | 1,017 | -0.3% | 1,692 | 1 | Village |
| Martinsburg | 19 | 222 | 224 | 0% | 1,254 | 0 | Village |
Mount Vernon is the largest city in Knox County, with a population of 17,462.
Martinsburg is the smallest city in Knox County, with a population of 222.
There are 19 cities in Knox County, Ohio.