5 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Belvidere | 1 | 25,352 | 25,271 | 0.06% | 1,984 | 13 | City |
| Poplar Grove | 2 | 5,215 | 5,065 | 0.48% | 662 | 8 | Village |
| Capron | 3 | 1,409 | 1,387 | 0.28% | 1,825 | 1 | Village |
| Timberlane | 4 | 900 | 905 | -0.11% | 515 | 2 | Village |
| Caledonia | 5 | 181 | 184 | 0% | 175 | 1 | Village |
Belvidere is the largest city in Boone County, with a population of 25,352.
Caledonia is the smallest city in Boone County, with a population of 181.
There are 5 cities in Boone County, Illinois.