34 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Galesburg City township | 1 | 28,892 | 29,944 | -0.41% | 1,627 | 17.76 | Township |
| Galesburg | 2 | 28,587 | 29,944 | -0.94% | 1,610 | 17.76 | City |
| Knox township | 3 | 4,754 | 4,921 | -0.38% | 134 | 35.41 | Township |
| Cedar township | 4 | 2,931 | 3,053 | -0.51% | 81 | 36.01 | Township |
| Abingdon | 5 | 2,788 | 2,945 | -1.1% | 1,956 | 1.43 | City |
| Knoxville | 6 | 2,764 | 2,891 | -0.9% | 1,176 | 2.35 | City |
| Indian Point township | 7 | 1,387 | 1,446 | -0.5% | 38 | 36.09 | Township |
| Henderson township | 8 | 1,096 | 1,140 | -0.54% | 32 | 33.81 | Township |
| Persifer township | 9 | 1,050 | 1,083 | -0.28% | 30 | 34.73 | Township |
| Ontario township | 10 | 876 | 915 | -0.68% | 24 | 36.19 | Township |
| Truro township | 11 | 818 | 853 | -0.61% | 23 | 35.73 | Township |
| East Galesburg | 12 | 726 | 761 | -0.95% | 532 | 1.36 | Village |
| Oak Run | 13 | 704 | 468 | 1.44% | 165 | 4.28 | CDP |
| Wataga | 14 | 700 | 740 | -1.13% | 844 | 0.83 | Village |
| Oneida | 15 | 661 | 696 | -1.05% | 866 | 0.76 | City |
| Walnut Grove township | 16 | 653 | 677 | -0.31% | 18 | 35.56 | Township |
| Yates City | 17 | 610 | 642 | -0.97% | 1,237 | 0.49 | Village |
| Williamsfield | 18 | 540 | 569 | -1.1% | 439 | 1.23 | Village |
| Orange township | 19 | 507 | 525 | -0.39% | 14 | 36.16 | Township |
| Rio township | 20 | 493 | 514 | -0.6% | 14 | 36.14 | Township |
| Maquon township | 21 | 450 | 463 | 0% | 13 | 35.88 | Township |
| Altona | 22 | 437 | 462 | -1.13% | 466 | 0.94 | Village |
| Galesburg township | 23 | 379 | 389 | -0.26% | 18 | 21.35 | Township |
| Copley township | 24 | 376 | 394 | -0.79% | 11 | 35.07 | Township |
| Victoria township | 25 | 351 | 368 | -0.85% | 10 | 35 | Township |
| Haw Creek township | 26 | 340 | 358 | -0.87% | 10 | 35.77 | Township |
| Lynn township | 27 | 253 | 268 | -1.17% | 7 | 35.32 | Township |
| Henderson | 28 | 251 | 263 | -0.79% | 947 | 0.27 | Village |
| Victoria | 29 | 249 | 268 | -1.58% | 552 | 0.45 | Village |
| Elba township | 30 | 246 | 255 | -0.4% | 7 | 36.34 | Township |
| Maquon | 31 | 210 | 222 | -0.94% | 1,296 | 0.16 | Village |
| Rio | 32 | 200 | 209 | -0.99% | 641 | 0.31 | Village |
| St. Augustine | 33 | 110 | 117 | -0.9% | 185 | 0.59 | Village |
| Gilson | 34 | 104 | 194 | -5.45% | 314 | 0.33 | CDP |
Galesburg City township is the largest city in Knox County, with a population of 28,892.
Gilson is the smallest city in Knox County.
There are 34 cities in Knox County, Illinois.