| City | State | 2026 Pop. ↓ | Annual Change | Rank | Type |
|---|---|---|---|---|---|
| Denver | Colorado | 746,590 | 0.81% | 1 | City |
| Colorado Springs | Colorado | 497,549 | 0.57% | 2 | City |
| Aurora | Colorado | 415,462 | 1.32% | 3 | City |
| Boise City | Idaho | 238,853 | 0.18% | 4 | City |
| Fort Collins | Colorado | 171,693 | 0.11% | 5 | City |
| Lakewood | Colorado | 157,210 | 0.18% | 6 | City |
| Thornton | Colorado | 149,318 | 1.05% | 7 | City |
| Meridian | Idaho | 148,009 | 3.51% | 8 | City |
| Nampa | Idaho | 124,426 | 3.36% | 9 | City |
| Arvada | Colorado | 122,391 | -0.41% | 10 | City |
| Billings | Montana | 122,295 | 0.87% | 11 | City |
| Greeley | Colorado | 116,451 | 1.2% | 12 | City |
| Westminster | Colorado | 116,095 | -0.07% | 13 | City |
| Pueblo | Colorado | 110,269 | -0.12% | 14 | City |
| Centennial | Colorado | 109,178 | 0.48% | 15 | City |
| Boulder | Colorado | 105,220 | -0.44% | 16 | City |
| Highlands Ranch | Colorado | 102,527 | 0.36% | 17 | CDP |
| Longmont | Colorado | 100,211 | 0.1% | 18 | City |
| Castle Rock | Colorado | 86,094 | 2.72% | 19 | Town |
| Loveland | Colorado | 82,545 | 1.42% | 20 | City |
| Broomfield | Colorado | 80,154 | 1.24% | 21 | City |
| Missoula | Montana | 79,837 | 1.18% | 22 | City |
| Caldwell | Idaho | 79,746 | 4.07% | 23 | City |
| Commerce City | Colorado | 74,414 | 2.86% | 24 | City |
| Grand Junction | Colorado | 73,036 | 1.68% | 25 | City |
| Idaho Falls | Idaho | 72,700 | 1.27% | 26 | City |
| Parker | Colorado | 67,604 | 2.45% | 27 | Town |
| Cheyenne | Wyoming | 66,580 | 0.11% | 28 | City |
| Great Falls | Montana | 60,117 | -0.15% | 29 | City |
| Bozeman | Montana | 59,872 | 1.8% | 30 | City |
| Pocatello | Idaho | 59,205 | 0.74% | 31 | City |
| Coeur d'Alene | Idaho | 58,785 | 1.04% | 32 | City |
| Casper | Wyoming | 58,624 | -0.25% | 33 | City |
| Twin Falls | Idaho | 57,077 | 1.53% | 34 | City |