23 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Mount Vernon | 1 | 16,286 | 16,948 | -0.8% | 1,674 | 9.73 | City |
| Howard township | 2 | 5,989 | 5,882 | 0.12% | 266 | 22.55 | Township |
| Apple Valley | 3 | 5,257 | 5,538 | 0.25% | 874 | 6.01 | CDP |
| Hilliar township | 4 | 3,850 | 3,786 | 0.5% | 148 | 25.97 | Township |
| College township | 5 | 2,720 | 2,551 | 1.04% | 433 | 6.29 | Township |
| Fredericktown | 6 | 2,599 | 2,648 | -0.38% | 1,310 | 1.98 | Village |
| Union township | 7 | 2,541 | 2,630 | -0.7% | 85 | 30.03 | Township |
| Gambier | 8 | 2,403 | 2,220 | 1.56% | 2,565 | 0.94 | Village |
| Brown township | 9 | 2,075 | 2,053 | 0.1% | 69 | 29.93 | Township |
| Morris township | 10 | 2,055 | 2,107 | -0.53% | 98 | 20.88 | Township |
| Liberty township | 11 | 1,941 | 1,930 | -0.1% | 76 | 25.68 | Township |
| Pleasant township | 12 | 1,665 | 1,668 | -0.12% | 93 | 17.95 | Township |
| Pike township | 13 | 1,661 | 1,674 | -0.36% | 55 | 30.38 | Township |
| Centerburg | 14 | 1,656 | 1,693 | -0.42% | 1,713 | 0.97 | Village |
| Clay township | 15 | 1,491 | 1,552 | -0.93% | 59 | 25.09 | Township |
| Middlebury township | 16 | 1,416 | 1,397 | 0.21% | 69 | 20.52 | Township |
| Morgan township | 17 | 1,078 | 1,066 | 0.09% | 41 | 26.02 | Township |
| South Mount Vernon | 18 | 1,066 | 778 | 7.14% | 2,111 | 0.51 | CDP |
| Miller township | 19 | 1,047 | 1,054 | -0.29% | 50 | 20.74 | Township |
| Danville | 20 | 981 | 1,018 | -0.71% | 1,660 | 0.59 | Village |
| Howard | 21 | 518 | 177 | 3.6% | 2,313 | 0.22 | CDP |
| Bladensburg | 22 | 281 | 353 | 2.18% | 852 | 0.33 | CDP |
| Martinsburg | 23 | 218 | 225 | -0.46% | 1,232 | 0.18 | Village |
Mount Vernon is the largest city in Knox County, with a population of 16,286.
Martinsburg is the smallest city in Knox County.
There are 23 cities in Knox County, Ohio.