| County | County seat | 2024 population | Land (sq mi) |
|---|---|---|---|
| Caldwell | Kingston | 9,000 | 426.39 |
| Carroll | Carrollton | 8,414 | 694.62 |
| Chariton | Keytesville | 7,397 | 751.18 |
| Daviess | Gallatin | 8,541 | 563.28 |
| Grundy | Trenton | 9,766 | 435.29 |
| Harrison | Bethany | 8,186 | 722.52 |
| Linn | Linneus | 11,910 | 615.59 |
| Livingston | Chillicothe | 14,658 | 532.30 |
| Mercer | Princeton | 3,452 | 453.83 |
| Putnam | Unionville | 4,539 | 517.32 |
| Sullivan | Milan | 5,750 | 647.98 |