37 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Flagg township | 1 | 13,112 | 13,303 | -0.21% | 369 | 35.55 | Township |
| Rochelle | 2 | 9,243 | 9,432 | -0.41% | 672 | 13.76 | City |
| Byron township | 3 | 6,414 | 6,432 | 0.05% | 175 | 36.66 | Township |
| Oregon-Nashua township | 4 | 4,715 | 4,804 | -0.32% | 123 | 38.44 | Township |
| Byron | 5 | 3,764 | 3,784 | -0.11% | 809 | 4.65 | City |
| Mount Morris township | 6 | 3,636 | 3,703 | -0.3% | 101 | 36.12 | Township |
| Oregon | 7 | 3,532 | 3,616 | -0.48% | 1,833 | 1.93 | City |
| Scott township | 8 | 3,334 | 3,295 | 0.27% | 93 | 35.92 | Township |
| Mount Morris | 9 | 2,783 | 2,848 | -0.46% | 1,784 | 1.56 | Village |
| Davis Junction | 10 | 2,554 | 2,511 | 0.35% | 608 | 4.20 | Village |
| Polo | 11 | 2,232 | 2,281 | -0.45% | 1,538 | 1.45 | City |
| Forreston township | 12 | 1,949 | 1,988 | -0.31% | 54 | 36.34 | Township |
| Westlake Village | 13 | 1,808 | 1,744 | 7.17% | 1,963 | 0.92 | CDP |
| Rockvale township | 14 | 1,764 | 1,778 | -0.11% | 51 | 34.77 | Township |
| Monroe township | 15 | 1,419 | 1,442 | -0.35% | 39 | 36.12 | Township |
| Forreston | 16 | 1,395 | 1,432 | -0.5% | 1,479 | 0.94 | Village |
| Leaf River township | 17 | 1,073 | 1,089 | -0.19% | 30 | 35.81 | Township |
| Stillman Valley | 18 | 1,052 | 1,072 | -0.38% | 1,846 | 0.57 | Village |
| Dement township | 19 | 939 | 955 | -0.21% | 27 | 34.99 | Township |
| Pine Rock township | 20 | 936 | 944 | -0.11% | 24 | 38.22 | Township |
| Taylor township | 21 | 917 | 925 | -0.11% | 60 | 15.24 | Township |
| New Milford | 22 | 788 | 793 | -0.13% | 305 | 2.58 | Village |
| Pine Creek township | 23 | 697 | 706 | -0.29% | 18 | 39.69 | Township |
| White Rock township | 24 | 683 | 692 | -0.15% | 19 | 35.51 | Township |
| Grand Detour township | 25 | 647 | 656 | -0.31% | 59 | 10.99 | Township |
| Creston | 26 | 613 | 627 | -0.49% | 535 | 1.15 | Village |
| Lynnville township | 27 | 567 | 574 | -0.18% | 16 | 34.87 | Township |
| Maryland township | 28 | 502 | 509 | -0.2% | 14 | 35.97 | Township |
| Leaf River | 29 | 419 | 429 | -0.48% | 482 | 0.87 | Village |
| Monroe Center | 30 | 402 | 412 | -0.5% | 332 | 1.21 | Village |
| Woosung township | 31 | 344 | 349 | -0.29% | 19 | 17.70 | Township |
| Brookville township | 32 | 234 | 238 | -0.43% | 13 | 18.08 | Township |
| Holcomb | 33 | 209 | 157 | 7.18% | 2,348 | 0.09 | CDP |
| Eagle Point township | 34 | 191 | 193 | 0% | 10 | 19.57 | Township |
| Baileyville | 35 | 171 | 126 | 6.88% | 707 | 0.24 | CDP |
| Lafayette township | 36 | 146 | 150 | -0.68% | 8 | 17.46 | Township |
| Adeline | 37 | 74 | 76 | 0% | 278 | 0.27 | Village |
Flagg township is the largest city in Ogle County, with a population of 13,112.
Adeline is the smallest city in Ogle County.
There are 37 cities in Ogle County, Illinois.