31 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Sterling | 1 | 16,999 | 17,317 | 0.08% | 727 | 23 | Township |
| Sterling | 2 | 14,459 | 14,837 | -0.52% | 2,432 | 6 | City |
| Coloma | 3 | 10,391 | 10,560 | 0.07% | 1,035 | 10 | Township |
| Rock Falls | 4 | 8,574 | 8,771 | -0.46% | 2,153 | 4 | City |
| Mount Pleasant | 5 | 4,693 | 4,778 | 0.09% | 131 | 36 | Township |
| Fulton | 6 | 4,283 | 4,351 | 0.14% | 247 | 17 | Township |
| Morrison | 7 | 3,967 | 4,070 | -0.53% | 1,575 | 3 | City |
| Fulton | 8 | 3,564 | 3,647 | -0.47% | 1,524 | 2 | City |
| Prophetstown | 9 | 2,452 | 2,488 | 0.16% | 51 | 48 | Township |
| Montmorency | 10 | 2,418 | 2,439 | 0.29% | 68 | 36 | Township |
| Hopkins | 11 | 1,986 | 2,009 | 0.2% | 56 | 36 | Township |
| Prophetstown | 12 | 1,898 | 1,938 | -0.42% | 1,417 | 1 | City |
| Erie | 13 | 1,857 | 1,882 | 0.22% | 77 | 24 | Township |
| Erie | 14 | 1,485 | 1,515 | -0.4% | 1,076 | 1 | Village |
| Union Grove | 15 | 1,186 | 1,197 | 0.17% | 34 | 35 | Township |
| Albany | 16 | 1,007 | 1,017 | 0.1% | 81 | 12 | Township |
| Garden Plain | 17 | 976 | 986 | 0.21% | 32 | 31 | Township |
| Tampico | 18 | 975 | 996 | 0% | 27 | 36 | Township |
| Lyndon | 19 | 911 | 914 | 0.66% | 33 | 27 | Township |
| Albany | 20 | 848 | 861 | -0.35% | 792 | 1 | Village |
| Jordan | 21 | 843 | 853 | 0.24% | 24 | 36 | Township |
| Genesee | 22 | 702 | 712 | 0.14% | 20 | 35 | Township |
| Tampico | 23 | 670 | 692 | -0.74% | 1,701 | 0 | Village |
| Fenton | 24 | 561 | 564 | 0.54% | 16 | 35 | Township |
| Ustick | 25 | 535 | 542 | 0.19% | 15 | 35 | Township |
| Lyndon | 26 | 527 | 535 | -0.38% | 696 | 1 | Village |
| Portland | 27 | 428 | 433 | 0.23% | 12 | 35 | Township |
| Clyde | 28 | 397 | 399 | 0.25% | 11 | 36 | Township |
| Hahnaman | 29 | 352 | 350 | 0.86% | 10 | 36 | Township |
| Galt | 30 | 142 | 204 | 6.77% | 486 | 0 | CDP |
| Deer Grove | 31 | 39 | 36 | 0% | 95 | 0 | Village |
Sterling is the largest city in Whiteside County, with a population of 16,999.
Deer Grove is the smallest city in Whiteside County, with a population of 39.
There are 31 cities in Whiteside County, Illinois.