The largest county in Montana
There are two right answers. By land area it is Beaverhead County; by population it is Yellowstone County. Which one you want depends on what you meant by largest.
Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025. Retrieved 30 August 2026.
By land area
| Rank | Name | Land area | Population |
|---|---|---|---|
| 1 | Beaverhead County | 5,543 sq mi | 10,043 |
| 2 | Phillips County | 5,140 sq mi | 4,203 |
| 3 | Flathead County | 5,087 sq mi | 115,429 |
| 4 | Rosebud County | 5,008 sq mi | 8,253 |
| 5 | Big Horn County | 4,998 sq mi | 12,752 |
| 6 | Valley County | 4,926 sq mi | 7,385 |
| 7 | Garfield County | 4,677 sq mi | 1,148 |
| 8 | Fergus County | 4,339 sq mi | 11,825 |
| 9 | Blaine County | 4,228 sq mi | 6,860 |
| 10 | Chouteau County | 3,973 sq mi | 5,865 |
By population
| Rank | Name | Population | Density |
|---|---|---|---|
| 1 | Yellowstone County | 172,692 | 65.6 per sq mi |
| 2 | Gallatin County | 128,740 | 49.4 per sq mi |
| 3 | Missoula County | 123,513 | 47.6 per sq mi |
| 4 | Flathead County | 115,429 | 22.7 per sq mi |
| 5 | Cascade County | 85,029 | 31.5 per sq mi |
| 6 | Lewis and Clark County | 75,331 | 21.8 per sq mi |
| 7 | Ravalli County | 48,582 | 20.3 per sq mi |
| 8 | Silver Bow County | 36,118 | 50.3 per sq mi |
| 9 | Lake County | 33,392 | 22.4 per sq mi |
| 10 | Lincoln County | 22,328 | 6.2 per sq mi |
And the smallest
More on Montana
Rebuilt from source data 30 August 2026. How these figures are produced.