31 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Sterling township | 1 | 16,885 | 17,319 | -0.19% | 723 | 23.37 | Township |
| Sterling | 2 | 14,287 | 14,839 | -0.76% | 2,403 | 5.95 | City |
| Coloma township | 3 | 10,355 | 10,558 | -0.03% | 1,032 | 10.04 | Township |
| Rock Falls | 4 | 8,487 | 8,769 | -0.66% | 2,131 | 3.98 | City |
| Mount Pleasant township | 5 | 4,667 | 4,779 | -0.17% | 131 | 35.76 | Township |
| Fulton township | 6 | 4,247 | 4,351 | -0.19% | 244 | 17.37 | Township |
| Morrison | 7 | 3,923 | 4,067 | -0.73% | 1,558 | 2.52 | City |
| Fulton | 8 | 3,514 | 3,646 | -0.73% | 1,503 | 2.34 | City |
| Prophetstown township | 9 | 2,442 | 2,492 | -0.04% | 51 | 47.92 | Township |
| Montmorency township | 10 | 2,403 | 2,440 | 0% | 67 | 35.75 | Township |
| Hopkins township | 11 | 1,971 | 2,007 | -0.05% | 55 | 35.53 | Township |
| Prophetstown | 12 | 1,878 | 1,942 | -0.69% | 1,403 | 1.34 | City |
| Erie township | 13 | 1,846 | 1,884 | -0.05% | 77 | 23.99 | Township |
| Erie | 14 | 1,465 | 1,515 | -0.68% | 1,062 | 1.38 | Village |
| Union Grove township | 15 | 1,170 | 1,191 | -0.09% | 33 | 35.14 | Township |
| Albany township | 16 | 1,000 | 1,015 | 0% | 80 | 12.49 | Township |
| Tampico township | 17 | 972 | 998 | -0.21% | 27 | 35.73 | Township |
| Garden Plain township | 18 | 968 | 985 | 0% | 32 | 30.60 | Township |
| Lyndon township | 19 | 903 | 914 | 0% | 33 | 27.32 | Township |
| Albany | 20 | 838 | 857 | -0.48% | 782 | 1.07 | Village |
| Jordan township | 21 | 838 | 853 | 0% | 23 | 35.84 | Township |
| Genesee township | 22 | 687 | 702 | -0.15% | 19 | 35.42 | Township |
| Tampico | 23 | 664 | 693 | -0.9% | 1,685 | 0.39 | Village |
| Fenton township | 24 | 553 | 563 | 0% | 16 | 34.88 | Township |
| Ustick township | 25 | 530 | 542 | -0.19% | 15 | 35.44 | Township |
| Lyndon | 26 | 518 | 535 | -0.58% | 684 | 0.76 | Village |
| Portland township | 27 | 417 | 424 | 0% | 12 | 34.70 | Township |
| Clyde township | 28 | 404 | 411 | 0% | 11 | 35.84 | Township |
| Hahnaman township | 29 | 350 | 350 | 0.57% | 10 | 35.79 | Township |
| Galt | 30 | 142 | 204 | 6.77% | 486 | 0.29 | CDP |
| Deer Grove | 31 | 37 | 36 | 0% | 90 | 0.41 | Village |
Sterling township is the largest city in Whiteside County, with a population of 16,885.
Deer Grove is the smallest city in Whiteside County.
There are 31 cities in Whiteside County, Illinois.