| County | Rank | Change (2020) ↓ | 2025 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Broadwater County | 1 | 24.69% | 8,554 | 6,860 |
| Petroleum County | 2 | 24.25% | 620 | 499 |
| Musselshell County | 3 | 17.6% | 5,586 | 4,750 |
| Madison County | 4 | 16.14% | 10,059 | 8,661 |
| Lincoln County | 5 | 14.85% | 22,665 | 19,734 |
| Sanders County | 6 | 14.66% | 14,284 | 12,458 |
| Mineral County | 7 | 14.49% | 5,230 | 4,568 |
| Granite County | 8 | 14.46% | 3,791 | 3,312 |
| Meagher County | 9 | 12.55% | 2,161 | 1,920 |
| Carbon County | 10 | 12.18% | 11,785 | 10,505 |
| Flathead County | 11 | 11.81% | 117,267 | 104,876 |
| Jefferson County | 12 | 11.04% | 13,482 | 12,142 |
| Ravalli County | 13 | 10.02% | 48,860 | 44,411 |
| Lake County | 14 | 9.76% | 34,308 | 31,258 |
| Lewis and Clark County | 15 | 8.83% | 77,465 | 71,177 |
| Beaverhead County | 16 | 8.3% | 10,161 | 9,382 |
| Gallatin County | 17 | 8.16% | 129,351 | 119,597 |
| Treasure County | 18 | 6.46% | 808 | 759 |
| Park County | 19 | 5.69% | 18,203 | 17,223 |
| Silver Bow County | 20 | 5.61% | 37,186 | 35,210 |
| Teton County | 21 | 5.53% | 6,598 | 6,252 |
| Toole County | 22 | 5.49% | 5,245 | 4,972 |
| Deer Lodge County | 23 | 5.42% | 9,931 | 9,420 |
| Pondera County | 24 | 5.32% | 6,191 | 5,878 |
| Judith Basin County | 25 | 5% | 2,121 | 2,020 |
| Yellowstone County | 26 | 4.58% | 172,789 | 165,218 |
| Sweet Grass County | 27 | 4.5% | 3,835 | 3,670 |
| Missoula County | 28 | 4.38% | 123,525 | 118,347 |
| Powell County | 29 | 4.34% | 7,243 | 6,942 |
| Fergus County | 30 | 4.33% | 11,972 | 11,475 |
| Powder River County | 31 | 4.07% | 1,765 | 1,696 |
| Golden Valley County | 32 | 3.9% | 853 | 821 |
| Carter County | 33 | 3.13% | 1,448 | 1,404 |
| Prairie County | 34 | 2.66% | 1,120 | 1,091 |
| Garfield County | 35 | 2.13% | 1,197 | 1,172 |
| Stillwater County | 36 | 1.98% | 9,181 | 9,003 |
| Hill County | 37 | 1.97% | 16,592 | 16,271 |
| Phillips County | 38 | 1.85% | 4,291 | 4,213 |
| Liberty County | 39 | 1.02% | 1,974 | 1,954 |
| Wheatland County | 40 | 0.92% | 2,095 | 2,076 |
| Custer County | 41 | 0.75% | 11,955 | 11,866 |
| Cascade County | 42 | 0.34% | 84,698 | 84,407 |
| Dawson County | 43 | -1.21% | 8,816 | 8,924 |
| Glacier County | 44 | -1.59% | 13,527 | 13,745 |
| Rosebud County | 45 | -1.6% | 8,176 | 8,309 |
| Daniels County | 46 | -2.72% | 1,609 | 1,654 |
| Valley County | 47 | -2.89% | 7,338 | 7,556 |
| Chouteau County | 48 | -2.95% | 5,725 | 5,899 |
| Blaine County | 49 | -3.62% | 6,753 | 7,007 |
| Big Horn County | 50 | -3.66% | 12,601 | 13,080 |
| Richland County | 51 | -4.12% | 11,059 | 11,534 |
| Sheridan County | 52 | -4.41% | 3,384 | 3,540 |
| Fallon County | 53 | -4.85% | 2,882 | 3,029 |
| Wibaux County | 54 | -6.31% | 876 | 935 |
| McCone County | 55 | -7.06% | 1,606 | 1,728 |
| Roosevelt County | 56 | -8.5% | 9,883 | 10,801 |
Montana's counties show varied growth patterns from 2020 to 2025. Broadwater County leads with 24.69% annualized growth, followed by Petroleum County (24.25%) and Musselshell County (17.6%). The largest counties are Yellowstone County (172,789), Gallatin County (129,351), and Missoula County (123,525). Of the 56 counties in Montana, 42 are growing while 14 have experienced population decline. Overall, counties averaged 4.82% annualized growth, with total population growing by 6.02% annually.