| County | Rank | Change (2020) ↓ | 2026 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Broadwater County | 1 | 26.78% | 8,697 | 6,860 |
| Musselshell County | 2 | 20.3% | 5,712 | 4,748 |
| Madison County | 3 | 18.75% | 10,280 | 8,657 |
| Sanders County | 4 | 14.28% | 14,232 | 12,454 |
| Lincoln County | 5 | 14.04% | 22,509 | 19,737 |
| Mineral County | 6 | 13.49% | 5,183 | 4,567 |
| Meagher County | 7 | 13.37% | 2,179 | 1,922 |
| Granite County | 8 | 11.19% | 3,677 | 3,307 |
| Petroleum County | 9 | 11.16% | 558 | 502 |
| Flathead County | 10 | 11.08% | 116,491 | 104,873 |
| Ravalli County | 11 | 10.62% | 49,127 | 44,412 |
| Jefferson County | 12 | 10.59% | 13,427 | 12,141 |
| Judith Basin County | 13 | 9.09% | 2,209 | 2,025 |
| Carbon County | 14 | 8.72% | 11,428 | 10,511 |
| Gallatin County | 15 | 8.69% | 129,982 | 119,593 |
| Beaverhead County | 16 | 7.69% | 10,096 | 9,375 |
| Lake County | 17 | 6.9% | 33,401 | 31,245 |
| Powder River County | 18 | 6.49% | 1,804 | 1,694 |
| Lewis and Clark County | 19 | 6.17% | 75,570 | 71,181 |
| Toole County | 20 | 6.08% | 5,269 | 4,967 |
| Park County | 21 | 5.96% | 18,255 | 17,229 |
| Missoula County | 22 | 5.25% | 124,555 | 118,337 |
| Yellowstone County | 23 | 5.22% | 173,836 | 165,208 |
| Stillwater County | 24 | 5.15% | 9,461 | 8,998 |
| Teton County | 25 | 4.81% | 6,553 | 6,252 |
| Powell County | 26 | 3.63% | 7,193 | 6,941 |
| Pondera County | 27 | 3.33% | 6,079 | 5,883 |
| Wheatland County | 28 | 3.23% | 2,142 | 2,075 |
| Fergus County | 29 | 3.06% | 11,824 | 11,473 |
| Golden Valley County | 30 | 2.68% | 844 | 822 |
| Silver Bow County | 31 | 2.66% | 36,145 | 35,208 |
| Deer Lodge County | 32 | 2.41% | 9,652 | 9,425 |
| Prairie County | 33 | 2.01% | 1,116 | 1,094 |
| Custer County | 34 | 1.95% | 12,091 | 11,860 |
| Richland County | 35 | 1.35% | 11,683 | 11,527 |
| Cascade County | 36 | 1.16% | 85,390 | 84,410 |
| Sweet Grass County | 37 | 0.87% | 3,706 | 3,674 |
| Liberty County | 38 | 0.36% | 1,963 | 1,956 |
| Phillips County | 39 | 0.05% | 4,210 | 4,208 |
| Hill County | 40 | -0.18% | 16,219 | 16,248 |
| Rosebud County | 41 | -0.25% | 8,288 | 8,309 |
| McCone County | 42 | -0.35% | 1,725 | 1,731 |
| Chouteau County | 43 | -0.58% | 5,877 | 5,911 |
| Fallon County | 44 | -2.34% | 2,958 | 3,029 |
| Blaine County | 45 | -2.35% | 6,844 | 7,009 |
| Glacier County | 46 | -2.37% | 13,411 | 13,736 |
| Valley County | 47 | -2.37% | 7,385 | 7,564 |
| Dawson County | 48 | -3.09% | 8,645 | 8,921 |
| Big Horn County | 49 | -3.23% | 12,657 | 13,079 |
| Sheridan County | 50 | -4.12% | 3,394 | 3,540 |
| Daniels County | 51 | -4.18% | 1,581 | 1,650 |
| Garfield County | 52 | -4.19% | 1,121 | 1,170 |
| Carter County | 53 | -4.41% | 1,344 | 1,406 |
| Treasure County | 54 | -4.88% | 721 | 758 |
| Roosevelt County | 55 | -4.94% | 10,274 | 10,808 |
| Wibaux County | 56 | -8.33% | 858 | 936 |
Montana's counties show varied growth patterns from 2020 to 2026. Broadwater County leads with 4.03% annualized growth, followed by Musselshell County (3.13%) and Madison County (2.91%). The largest counties are Yellowstone County (173,836), Gallatin County (129,982), and Missoula County (124,555). Of the 56 counties in Montana, 39 are growing while 17 have experienced population decline. Overall, counties averaged 0.67% annualized growth, with total population growing by 0.97% annually.
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