17 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Grafton township | 1 | 57,503 | 56,441 | 0.37% | 1,611 | 35.69 | Township |
| Jersey township | 2 | 9,844 | 9,986 | -0.07% | 210 | 46.96 | Township |
| Jerseyville | 3 | 8,223 | 8,323 | -0.24% | 1,570 | 5.24 | City |
| Elsah township | 4 | 2,050 | 2,166 | -1.06% | 86 | 23.87 | Township |
| Mississippi township | 5 | 1,668 | 1,787 | -1.36% | 46 | 36.36 | Township |
| Quarry township | 6 | 1,229 | 1,054 | 2.59% | 60 | 20.51 | Township |
| Grafton | 7 | 849 | 638 | 5.2% | 229 | 3.71 | City |
| Otter Creek township | 8 | 840 | 880 | -0.83% | 23 | 36.48 | Township |
| Fidelity township | 9 | 618 | 657 | -1.28% | 17 | 36.12 | Township |
| Elsah | 10 | 514 | 523 | -0.39% | 471 | 1.09 | Village |
| Richwood township | 11 | 483 | 522 | -1.63% | 13 | 37.56 | Township |
| English township | 12 | 441 | 478 | -1.78% | 12 | 36.92 | Township |
| Rosedale township | 13 | 388 | 412 | -1.27% | 13 | 30.26 | Township |
| Medora | 14 | 362 | 374 | -0.55% | 953 | 0.38 | Village |
| Ruyle township | 15 | 360 | 388 | -1.64% | 13 | 28.18 | Township |
| Fieldon | 16 | 160 | 175 | -1.84% | 792 | 0.20 | Village |
| Fidelity | 17 | 98 | 98 | 0% | 970 | 0.10 | Village |
Grafton township is the largest city in Jersey County, with a population of 57,503.
Fidelity is the smallest city in Jersey County.
There are 17 cities in Jersey County, Illinois.