| County | Rank | Change (2020) ↓ | 2026 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Broadwater County | 1 | 27.93% | 8,780 | 6,863 |
| Madison County | 2 | 18.24% | 10,241 | 8,661 |
| Musselshell County | 3 | 17.96% | 5,602 | 4,749 |
| Mineral County | 4 | 16.35% | 5,315 | 4,568 |
| Lincoln County | 5 | 15.57% | 22,818 | 19,744 |
| Sanders County | 6 | 14.22% | 14,233 | 12,461 |
| Jefferson County | 7 | 13.16% | 13,740 | 12,142 |
| Granite County | 8 | 11.19% | 3,676 | 3,306 |
| Flathead County | 9 | 11.17% | 116,591 | 104,881 |
| Carbon County | 10 | 10.73% | 11,642 | 10,514 |
| Ravalli County | 11 | 10.41% | 49,041 | 44,417 |
| Stillwater County | 12 | 9.71% | 9,876 | 9,002 |
| Beaverhead County | 13 | 9.2% | 10,240 | 9,377 |
| Meagher County | 14 | 8.16% | 2,081 | 1,924 |
| Gallatin County | 15 | 7.93% | 129,094 | 119,607 |
| Lake County | 16 | 7.85% | 33,699 | 31,247 |
| Deer Lodge County | 17 | 6.79% | 10,063 | 9,423 |
| Park County | 18 | 6.48% | 18,346 | 17,229 |
| Lewis and Clark County | 19 | 6.44% | 75,763 | 71,179 |
| Judith Basin County | 20 | 5.54% | 2,135 | 2,023 |
| Missoula County | 21 | 5.02% | 124,294 | 118,353 |
| Yellowstone County | 22 | 4.89% | 173,295 | 165,210 |
| Toole County | 23 | 4.75% | 5,203 | 4,967 |
| Fergus County | 24 | 4.22% | 11,954 | 11,470 |
| Golden Valley County | 25 | 4.14% | 855 | 821 |
| Teton County | 26 | 3.21% | 6,454 | 6,253 |
| McCone County | 27 | 3.12% | 1,783 | 1,729 |
| Sweet Grass County | 28 | 2.81% | 3,773 | 3,670 |
| Powder River County | 29 | 2.78% | 1,740 | 1,693 |
| Powell County | 30 | 2.57% | 7,116 | 6,938 |
| Pondera County | 31 | 2.4% | 6,018 | 5,877 |
| Silver Bow County | 32 | 2.29% | 36,016 | 35,210 |
| Prairie County | 33 | 1.47% | 1,106 | 1,090 |
| Rosebud County | 34 | 0.36% | 8,336 | 8,306 |
| Custer County | 35 | 0.03% | 11,866 | 11,863 |
| Cascade County | 36 | -0.11% | 84,319 | 84,411 |
| Chouteau County | 37 | -0.52% | 5,886 | 5,917 |
| Carter County | 38 | -0.71% | 1,397 | 1,407 |
| Blaine County | 39 | -0.89% | 6,941 | 7,003 |
| Wibaux County | 40 | -1.18% | 925 | 936 |
| Phillips County | 41 | -1.54% | 4,146 | 4,211 |
| Wheatland County | 42 | -1.64% | 2,038 | 2,072 |
| Daniels County | 43 | -1.81% | 1,623 | 1,653 |
| Hill County | 44 | -2.58% | 15,833 | 16,253 |
| Petroleum County | 45 | -2.59% | 489 | 502 |
| Big Horn County | 46 | -2.64% | 12,738 | 13,083 |
| Valley County | 47 | -2.76% | 7,352 | 7,561 |
| Glacier County | 48 | -2.83% | 13,355 | 13,744 |
| Liberty County | 49 | -3.78% | 1,884 | 1,958 |
| Dawson County | 50 | -4.14% | 8,553 | 8,922 |
| Sheridan County | 51 | -4.86% | 3,364 | 3,536 |
| Garfield County | 52 | -5.12% | 1,111 | 1,171 |
| Richland County | 53 | -5.53% | 10,896 | 11,534 |
| Fallon County | 54 | -6.24% | 2,840 | 3,029 |
| Roosevelt County | 55 | -8.01% | 9,937 | 10,802 |
| Treasure County | 56 | -9.89% | 683 | 758 |
Montana's counties show varied growth patterns from 2020 to 2026. Broadwater County leads with 4.19% annualized growth, followed by Madison County (2.83%) and Musselshell County (2.79%). The largest counties are Yellowstone County (173,295), Gallatin County (129,094), and Missoula County (124,294). Of the 56 counties in Montana, 35 are growing while 21 have experienced population decline. Overall, counties averaged 0.58% annualized growth, with total population growing by 0.93% annually.
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