| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Belvidere | 1 | 25,500 | 25,274 | 0.15% | 1,996 | 13 | City |
| Poplar Grove | 2 | 5,236 | 5,060 | 0.58% | 665 | 8 | Village |
| Capron | 3 | 1,412 | 1,388 | 0.36% | 1,829 | 1 | Village |
| Timberlane | 4 | 908 | 905 | 0% | 520 | 2 | Village |
| Caledonia | 5 | 182 | 184 | -0.55% | 176 | 1 | Village |
Belvidere is the largest city in Boone County, with a population of 25,500.
Caledonia is the smallest city in Boone County, with a population of 182.
There are 5 cities in Boone County, Illinois.