10 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Morgan | 1 | 1,355 | 1,420 | -1.45% | 26 | 51 | Township |
| Princeton | 2 | 974 | 1,000 | -0.41% | 613 | 2 | City |
| Marion | 3 | 691 | 717 | -1.14% | 13 | 52 | Township |
| Mercer | 4 | 257 | 262 | -0.39% | 698 | 0 | Town |
| Harrison | 5 | 205 | 212 | -0.97% | 5 | 44 | Township |
| Ravanna | 6 | 186 | 197 | -1.59% | 3 | 57 | Township |
| Medicine | 7 | 126 | 138 | -3.08% | 3 | 49 | Township |
| Lindley | 8 | 108 | 111 | -0.92% | 2 | 58 | Township |
| Somerset | 9 | 86 | 90 | -1.15% | 2 | 44 | Township |
| South Lineville | 10 | 13 | 13 | 0% | 241 | 0 | Town |
Morgan is the largest city in Mercer County, with a population of 1,355.
South Lineville is the smallest city in Mercer County, with a population of 13.
There are 10 cities in Mercer County, Missouri.