17 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Grafton | 1 | 57,882 | 56,447 | 0.61% | 1,622 | 36 | Township |
| Jersey | 2 | 9,992 | 9,986 | 0.5% | 213 | 47 | Township |
| Jerseyville | 3 | 8,356 | 8,323 | 0.07% | 1,596 | 5 | City |
| Elsah | 4 | 2,072 | 2,159 | -0.53% | 87 | 24 | Township |
| Mississippi | 5 | 1,698 | 1,784 | -0.64% | 47 | 36 | Township |
| Quarry | 6 | 1,167 | 1,057 | -0.26% | 57 | 21 | Township |
| Otter Creek | 7 | 842 | 874 | -0.59% | 23 | 36 | Township |
| Grafton | 8 | 803 | 646 | 4.02% | 216 | 4 | City |
| Fidelity | 9 | 628 | 657 | -0.48% | 17 | 36 | Township |
| Elsah | 10 | 517 | 525 | -0.39% | 473 | 1 | Village |
| Richwood | 11 | 492 | 521 | -0.81% | 13 | 38 | Township |
| English | 12 | 470 | 489 | -0.21% | 13 | 37 | Township |
| Rosedale | 13 | 397 | 413 | -0.25% | 13 | 30 | Township |
| Ruyle | 14 | 367 | 386 | -0.54% | 13 | 28 | Township |
| Medora | 15 | 362 | 371 | -0.55% | 953 | 0 | Village |
| Fieldon | 16 | 159 | 171 | -1.85% | 787 | 0 | Village |
| Fidelity | 17 | 93 | 97 | -1.06% | 921 | 0 | Village |
Grafton is the largest city in Jersey County, with a population of 57,882.
Fidelity is the smallest city in Jersey County, with a population of 93.
There are 17 cities in Jersey County, Illinois.