12 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Belvidere | 1 | 29,367 | 29,359 | 0.09% | 813 | 36 | Township |
| Belvidere | 2 | 25,338 | 25,271 | 0.05% | 1,983 | 13 | City |
| Caledonia | 3 | 7,229 | 7,273 | 0.11% | 300 | 24 | Township |
| Poplar Grove | 4 | 5,192 | 5,120 | 0.39% | 218 | 24 | Township |
| Poplar Grove | 5 | 5,190 | 5,065 | 0.48% | 659 | 8 | Village |
| Bonus | 6 | 4,375 | 4,376 | 0.09% | 123 | 36 | Township |
| Boone | 7 | 2,029 | 2,014 | 0.5% | 85 | 24 | Township |
| Capron | 8 | 1,405 | 1,387 | 0.21% | 1,820 | 1 | Village |
| Timberlane | 9 | 901 | 905 | -0.11% | 516 | 2 | Village |
| Spring | 10 | 858 | 868 | 0.12% | 24 | 36 | Township |
| LeRoy | 11 | 466 | 471 | 0.22% | 15 | 31 | Township |
| Caledonia | 12 | 181 | 184 | -0.55% | 175 | 1 | Village |
Belvidere is the largest city in Boone County, with a population of 29,367.
Caledonia is the smallest city in Boone County, with a population of 181.
There are 12 cities in Boone County, Illinois.