40 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Quincy | 1 | 38,440 | 39,575 | -0.45% | 2,438 | 16 | Township |
| Quincy | 2 | 38,391 | 39,575 | -0.51% | 2,435 | 16 | City |
| Melrose | 3 | 5,436 | 5,639 | -0.59% | 121 | 45 | Township |
| Ellington | 4 | 2,684 | 2,805 | -0.67% | 78 | 34 | Township |
| Payson | 5 | 1,687 | 1,754 | -0.47% | 44 | 38 | Township |
| Camp Point | 6 | 1,598 | 1,627 | -0.13% | 43 | 38 | Township |
| Mendon | 7 | 1,363 | 1,428 | -0.8% | 37 | 37 | Township |
| Liberty | 8 | 1,313 | 1,374 | -0.76% | 36 | 37 | Township |
| Camp Point | 9 | 1,112 | 1,126 | -0.18% | 878 | 1 | Village |
| Gilmer | 10 | 1,110 | 1,160 | -0.63% | 30 | 37 | Township |
| Ursa | 11 | 1,072 | 1,121 | -0.65% | 19 | 57 | Township |
| Payson | 12 | 984 | 1,025 | -0.71% | 841 | 1 | Village |
| Clayton | 13 | 892 | 939 | -0.89% | 24 | 37 | Township |
| Burton | 14 | 879 | 918 | -0.68% | 23 | 38 | Township |
| Mendon | 15 | 831 | 869 | -0.72% | 970 | 1 | Village |
| Northeast | 16 | 811 | 843 | -0.49% | 22 | 37 | Township |
| Liberty | 17 | 727 | 735 | 0% | 40 | 18 | Township |
| Honey Creek | 18 | 696 | 730 | -0.71% | 19 | 37 | Township |
| Clayton | 19 | 629 | 638 | -0.16% | 18 | 36 | Township |
| Golden | 20 | 616 | 648 | -0.81% | 960 | 1 | Village |
| Clayton | 21 | 604 | 639 | -0.98% | 683 | 1 | Village |
| Keene | 22 | 582 | 606 | -0.68% | 16 | 36 | Township |
| Ursa | 23 | 578 | 607 | -0.86% | 838 | 1 | Village |
| Columbus | 24 | 541 | 567 | -0.73% | 14 | 37 | Township |
| Liberty | 25 | 514 | 540 | -0.77% | 1,315 | 0 | Village |
| Fall Creek | 26 | 509 | 529 | -0.59% | 14 | 36 | Township |
| Lima | 27 | 491 | 513 | -0.61% | 9 | 55 | Township |
| Richfield | 28 | 392 | 409 | -0.51% | 10 | 38 | Township |
| Beverly | 29 | 340 | 355 | -0.58% | 9 | 37 | Township |
| La Prairie | 30 | 335 | 345 | -0.89% | 9 | 36 | Township |
| Loraine | 31 | 291 | 300 | -0.34% | 345 | 1 | Village |
| Plainville | 32 | 255 | 270 | -0.78% | 1,085 | 0 | Village |
| Loraine | 33 | 249 | 256 | -0.4% | 7 | 35 | Township |
| Houston | 34 | 206 | 214 | -0.48% | 5 | 38 | Township |
| McKee | 35 | 171 | 184 | -1.72% | 5 | 36 | Township |
| Coatsburg | 36 | 147 | 153 | -0.68% | 1,114 | 0 | Village |
| Lima | 37 | 141 | 147 | -0.7% | 1,044 | 0 | Village |
| Columbus | 38 | 107 | 113 | -0.93% | 489 | 0 | Village |
| El Dara | 39 | 61 | 63 | 0% | 60 | 1 | Village |
| La Prairie | 40 | 39 | 41 | 0% | 202 | 0 | Village |
Quincy is the largest city in Adams County, with a population of 38,440.
La Prairie is the smallest city in Adams County, with a population of 39.
There are 40 cities in Adams County, Illinois.