23 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Mount Vernon | 1 | 17,395 | 17,063 | 0.38% | 1,788 | 10 | City |
| Howard | 2 | 6,141 | 5,882 | 0.66% | 272 | 23 | Township |
| Apple Valley | 3 | 5,257 | 5,538 | 0.25% | 874 | 6 | CDP |
| Hilliar | 4 | 3,875 | 3,787 | 0.1% | 149 | 26 | Township |
| College | 5 | 2,681 | 2,551 | 0.15% | 426 | 6 | Township |
| Fredericktown | 6 | 2,660 | 2,650 | 0.08% | 1,341 | 2 | Village |
| Union | 7 | 2,587 | 2,628 | -0.42% | 86 | 30 | Township |
| Gambier | 8 | 2,367 | 2,219 | 1.24% | 2,526 | 1 | Village |
| Brown | 9 | 2,118 | 2,054 | 0.38% | 71 | 30 | Township |
| Morris | 10 | 2,101 | 2,103 | 0.05% | 101 | 21 | Township |
| Liberty | 11 | 1,988 | 1,927 | 0.45% | 77 | 26 | Township |
| Centerburg | 12 | 1,700 | 1,703 | -0.06% | 1,758 | 1 | Village |
| Pike | 13 | 1,700 | 1,674 | 0% | 56 | 30 | Township |
| Pleasant | 14 | 1,698 | 1,667 | 0.24% | 95 | 18 | Township |
| Clay | 15 | 1,524 | 1,548 | -0.46% | 61 | 25 | Township |
| Middlebury | 16 | 1,434 | 1,397 | 0.14% | 70 | 21 | Township |
| Morgan | 17 | 1,105 | 1,066 | 0.64% | 42 | 26 | Township |
| Miller | 18 | 1,079 | 1,058 | 0.47% | 52 | 21 | Township |
| South Mount Vernon | 19 | 1,066 | 778 | 7.14% | 2,111 | 1 | CDP |
| Danville | 20 | 1,003 | 1,017 | -0.3% | 1,697 | 1 | Village |
| Howard | 21 | 518 | 177 | 3.6% | 2,313 | 0 | CDP |
| Bladensburg | 22 | 281 | 353 | 2.18% | 852 | 0 | CDP |
| Martinsburg | 23 | 222 | 224 | -0.45% | 1,254 | 0 | Village |
Mount Vernon is the largest city in Knox County, with a population of 17,395.
Martinsburg is the smallest city in Knox County, with a population of 222.
There are 23 cities in Knox County, Ohio.