| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Quincy | 1 | 38,740 | 39,564 | -0.46% | 2,457 | 16 | City |
| Camp Point | 2 | 1,116 | 1,126 | -0.27% | 882 | 1 | Village |
| Payson | 3 | 986 | 1,024 | -0.8% | 843 | 1 | Village |
| Mendon | 4 | 838 | 869 | -0.71% | 978 | 1 | Village |
| Golden | 5 | 623 | 651 | -0.95% | 970 | 1 | Village |
| Clayton | 6 | 610 | 637 | -0.97% | 690 | 1 | Village |
| Ursa | 7 | 598 | 622 | -0.83% | 867 | 1 | Village |
| Liberty | 8 | 517 | 539 | -0.96% | 1,322 | 0 | Village |
| Loraine | 9 | 287 | 297 | -0.69% | 340 | 1 | Village |
| Plainville | 10 | 258 | 269 | -0.77% | 1,098 | 0 | Village |
| Coatsburg | 11 | 150 | 155 | -0.66% | 1,136 | 0 | Village |
| Lima | 12 | 150 | 155 | -0.66% | 1,111 | 0 | Village |
| Columbus | 13 | 109 | 114 | -0.91% | 498 | 0 | Village |
| El Dara | 14 | 60 | 63 | -1.64% | 59 | 1 | Village |
| La Prairie | 15 | 39 | 41 | -2.5% | 202 | 0 | Village |
Quincy is the largest city in Adams County, with a population of 38,740.
La Prairie is the smallest city in Adams County, with a population of 39.
There are 15 cities in Adams County, Illinois.