15 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Quincy | 1 | 38,391 | 39,575 | -0.51% | 2,435 | 16 | City |
| Camp Point | 2 | 1,112 | 1,126 | -0.18% | 878 | 1 | Village |
| Payson | 3 | 984 | 1,025 | -0.71% | 841 | 1 | Village |
| Mendon | 4 | 831 | 869 | -0.72% | 970 | 1 | Village |
| Golden | 5 | 616 | 648 | -0.81% | 960 | 1 | Village |
| Clayton | 6 | 604 | 639 | -0.98% | 683 | 1 | Village |
| Ursa | 7 | 578 | 607 | -0.86% | 838 | 1 | Village |
| Liberty | 8 | 514 | 540 | -0.77% | 1,315 | 0 | Village |
| Loraine | 9 | 291 | 300 | -0.34% | 345 | 1 | Village |
| Plainville | 10 | 255 | 270 | -0.78% | 1,085 | 0 | Village |
| Coatsburg | 11 | 147 | 153 | -0.68% | 1,114 | 0 | Village |
| Lima | 12 | 141 | 147 | -0.7% | 1,044 | 0 | Village |
| Columbus | 13 | 107 | 113 | -0.93% | 489 | 0 | Village |
| El Dara | 14 | 61 | 63 | 0% | 60 | 1 | Village |
| La Prairie | 15 | 39 | 41 | 0% | 202 | 0 | Village |
Quincy is the largest city in Adams County, with a population of 38,391.
La Prairie is the smallest city in Adams County, with a population of 39.
There are 15 cities in Adams County, Illinois.