33 cities
| City | State | 2025 Pop. ↓ | Annual Change | Rank | Type |
|---|---|---|---|---|---|
| Denver | Colorado | 731,868 | 0.39% | 1 | City |
| Colorado Springs | Colorado | 496,514 | 0.6% | 2 | City |
| Aurora | Colorado | 407,211 | 1.01% | 3 | City |
| Boise City | Idaho | 238,443 | 0.2% | 4 | City |
| Fort Collins | Colorado | 171,157 | 0.14% | 5 | City |
| Lakewood | Colorado | 157,014 | 0.09% | 6 | City |
| Thornton | Colorado | 147,813 | 0.77% | 7 | City |
| Meridian | Idaho | 144,801 | 3.62% | 8 | City |
| Billings | Montana | 122,545 | 0.87% | 9 | City |
| Nampa | Idaho | 121,330 | 3.39% | 10 | City |
| Arvada | Colorado | 121,250 | -0.51% | 11 | City |
| Greeley | Colorado | 115,631 | 1.11% | 12 | City |
| Westminster | Colorado | 114,964 | -0.29% | 13 | City |
| Pueblo | Colorado | 110,980 | -0.17% | 14 | City |
| Centennial | Colorado | 109,015 | 0.15% | 15 | City |
| Boulder | Colorado | 106,399 | -0.38% | 16 | City |
| Longmont | Colorado | 99,971 | 0.15% | 17 | City |
| Castle Rock | Colorado | 85,544 | 2.8% | 18 | Town |
| Loveland | Colorado | 82,283 | 1.46% | 19 | City |
| Broomfield | Colorado | 79,280 | 1.22% | 20 | City |
| Missoula | Montana | 79,153 | 1.21% | 21 | City |
| Caldwell | Idaho | 76,174 | 4.22% | 22 | City |
| Commerce City | Colorado | 72,109 | 2.65% | 23 | City |
| Grand Junction | Colorado | 71,752 | 1.7% | 24 | City |
| Idaho Falls | Idaho | 70,421 | 1.29% | 25 | City |
| Parker | Colorado | 67,128 | 2.53% | 26 | Town |
| Cheyenne | Wyoming | 65,809 | 0.16% | 27 | City |
| Great Falls | Montana | 59,903 | -0.18% | 28 | City |
| Bozeman | Montana | 58,901 | 1.74% | 29 | City |
| Casper | Wyoming | 58,700 | -0.21% | 30 | City |
| Pocatello | Idaho | 58,680 | 0.77% | 31 | City |
| Coeur d'Alene | Idaho | 57,955 | 1.05% | 32 | City |
| Twin Falls | Idaho | 56,457 | 1.56% | 33 | City |