34 cities
| City | State | 2026 Pop. ↓ | Annual Change | Rank | Type |
|---|---|---|---|---|---|
| Denver | Colorado | 734,718 | 0.39% | 1 | City |
| Colorado Springs | Colorado | 499,474 | 0.6% | 2 | City |
| Aurora | Colorado | 411,293 | 1% | 3 | City |
| Boise City | Idaho | 238,923 | 0.2% | 4 | City |
| Fort Collins | Colorado | 171,391 | 0.14% | 5 | City |
| Lakewood | Colorado | 157,161 | 0.09% | 6 | City |
| Meridian | Idaho | 149,862 | 3.5% | 7 | City |
| Thornton | Colorado | 148,938 | 0.76% | 8 | City |
| Nampa | Idaho | 125,310 | 3.28% | 9 | City |
| Billings | Montana | 123,608 | 0.87% | 10 | City |
| Arvada | Colorado | 120,628 | -0.51% | 11 | City |
| Greeley | Colorado | 116,900 | 1.1% | 12 | City |
| Westminster | Colorado | 114,626 | -0.29% | 13 | City |
| Pueblo | Colorado | 110,794 | -0.17% | 14 | City |
| Centennial | Colorado | 109,178 | 0.15% | 15 | City |
| Boulder | Colorado | 105,995 | -0.38% | 16 | City |
| Highlands Ranch | Colorado | 102,527 | 0.36% | 17 | CDP |
| Longmont | Colorado | 100,124 | 0.15% | 18 | City |
| Castle Rock | Colorado | 87,875 | 2.72% | 19 | Town |
| Loveland | Colorado | 83,465 | 1.44% | 20 | City |
| Broomfield | Colorado | 80,237 | 1.21% | 21 | City |
| Missoula | Montana | 80,103 | 1.2% | 22 | City |
| Caldwell | Idaho | 79,260 | 4.05% | 23 | City |
| Commerce City | Colorado | 73,973 | 2.58% | 24 | City |
| Grand Junction | Colorado | 72,951 | 1.67% | 25 | City |
| Idaho Falls | Idaho | 71,320 | 1.28% | 26 | City |
| Parker | Colorado | 68,783 | 2.47% | 27 | Town |
| Cheyenne | Wyoming | 65,914 | 0.16% | 28 | City |
| Bozeman | Montana | 59,908 | 1.71% | 29 | City |
| Great Falls | Montana | 59,793 | -0.18% | 30 | City |
| Pocatello | Idaho | 59,129 | 0.77% | 31 | City |
| Casper | Wyoming | 58,577 | -0.21% | 32 | City |
| Coeur d'Alene | Idaho | 58,555 | 1.04% | 33 | City |
| Twin Falls | Idaho | 57,325 | 1.54% | 34 | City |