12 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Belvidere | 1 | 29,392 | 29,359 | 0.09% | 814 | 36 | Township |
| Belvidere | 2 | 25,352 | 25,271 | 0.06% | 1,984 | 13 | City |
| Caledonia | 3 | 7,237 | 7,273 | 0.11% | 301 | 24 | Township |
| Poplar Grove | 4 | 5,215 | 5,065 | 0.48% | 662 | 8 | Village |
| Poplar Grove | 5 | 5,212 | 5,120 | 0.39% | 219 | 24 | Township |
| Bonus | 6 | 4,379 | 4,376 | 0.09% | 123 | 36 | Township |
| Boone | 7 | 2,039 | 2,014 | 0.49% | 85 | 24 | Township |
| Capron | 8 | 1,409 | 1,387 | 0.28% | 1,825 | 1 | Village |
| Timberlane | 9 | 900 | 905 | -0.11% | 515 | 2 | Village |
| Spring | 10 | 859 | 868 | 0.12% | 24 | 36 | Township |
| LeRoy | 11 | 467 | 471 | 0.21% | 15 | 31 | Township |
| Caledonia | 12 | 181 | 184 | 0% | 175 | 1 | Village |
Belvidere is the largest city in Boone County, with a population of 29,392.
Caledonia is the smallest city in Boone County, with a population of 181.
There are 12 cities in Boone County, Illinois.