17 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Belvidere township | 1 | 29,531 | 29,361 | 0.4% | 818 | 36.10 | Township |
| Belvidere | 2 | 25,306 | 25,283 | 0.02% | 2,022 | 12.51 | City |
| Caledonia township | 3 | 7,170 | 7,278 | -0.28% | 298 | 24.06 | Township |
| Candlewick Lake | 4 | 6,350 | 5,351 | 7.14% | 3,434 | 1.85 | CDP |
| Poplar Grove | 5 | 5,177 | 5,056 | 0.47% | 657 | 7.88 | Village |
| Poplar Grove township | 6 | 5,165 | 5,113 | 0.23% | 217 | 23.77 | Township |
| Bonus township | 7 | 4,392 | 4,377 | 0.32% | 123 | 35.59 | Township |
| Boone township | 8 | 2,023 | 2,014 | 0.25% | 84 | 23.94 | Township |
| Capron | 9 | 1,399 | 1,388 | 0.14% | 1,812 | 0.77 | Village |
| Timberlane | 10 | 902 | 904 | 0% | 517 | 1.75 | Village |
| Spring township | 11 | 853 | 869 | -0.23% | 24 | 36.04 | Township |
| Argyle | 12 | 720 | 353 | 7.14% | 821 | 0.88 | CDP |
| LeRoy township | 13 | 458 | 469 | -0.43% | 15 | 31.26 | Township |
| Garden Prairie | 14 | 410 | 265 | 7.05% | 643 | 0.64 | CDP |
| Chemung | 15 | 406 | 738 | 1.75% | 1,445 | 0.28 | CDP |
| Lawrence | 16 | 251 | 150 | 7.26% | 682 | 0.37 | CDP |
| Caledonia | 17 | 178 | 182 | -0.56% | 172 | 1.03 | Village |
Belvidere township is the largest city in Boone County, with a population of 29,531.
Caledonia is the smallest city in Boone County.
There are 17 cities in Boone County, Illinois.