Colorado - Criteria: A (event)
| Independence and Independence Mill Site |
| Indian Grove |
| Indian Park School |
| Inspiration Point |
| IOOF Hall |
| Jackson, George, House |
| Jacobs Building |
| Jacoe Store |
| Jaffa Opera House |
| Jamaica Primary School |
| Jamestown Mercantile Building |
| Jamestown Town Hall |
| Jefferson Denver South Park and Pacific Railroad Depot |
| Joslin Dry Goods Company Building |
| Julien, Denis, Inscription |
| Keithley Log Cabin Development District |
| Kennicott Cabin |
| Key Savings and Loan Association Building |
| Keystone Hotel |
| Kissock Block Building |
| Kistler Stationery Company Building |
| Knearl School |
| Kopper's Hotel and Saloon |
| Kullgren House |
| Lafayette House |
| La Jara Depot |
| Lake Haiyaha Trail |
| Lamme Hospital |
| Land's End Observatory |
| Larimer Square |
| Las Animas Post Office |
| Laurel School Historic District |
| La Veta Pass Narrow Gauge Railroad Depot |
| Lay School |
| Leadville Historic District |
| Leadville National Fish Hatchery |
| Lebanon and Everett Mine Tunnels |
| Lebanon School |
| Leeman Auto Company Building |
| Lennox House |
| Lett Hotel |
| Lewis, A. T., and Son Department Store |
| Lewis House |
| Lewis, Inez Johnson, School |
| Lewis Mill |
| Limon Railroad Depot |
| Lincoln School |
| Lincoln School |
| Lincoln School |
| Little Thompson River Bridge |
| Littleton Creamery-Beatrice Foods Cold Storage Warehouse |
| Littleton Main Street |
| Loma Community Hall |
| Longmont Carnegie Library |
| Longmont College |
| Longmont Fire Department |
| Longmont Power Plant |
| Lookout Mountain Park |
| Loretto Heights Academy |
| Lost Lake Trail |
| Lost Trail Station |
| Louviers Village Club |
| Loveland Building and Coors Building |
| Loveland State Amory |
| Ludlow Tent Colony Site |
| Luft, Conrad, Sr., House |
| Lulu City Site |
| Lyons Railroad Depot |
| Macedonia Baptist Church |
| Main Avenue Historic District |
| Main Street Bridge |
| Maitland Arroyo Bridge |
| Mancos High School |
| Mancos Opera House |
| Manitou Bathhouse |
| Manitou Springs Historic District |
| Marble City State Bank Building |
| Marble High School |
| Marble Jailhouse |
| Marble Town Hall |
| Margery Building |
| Matchless Mine |
| Maxwell Building |
| Maysville School |
| McClelland Orphanage |
| McClintock Building |
| McGraw Ranch |
| McGregor Hall |
| McKenzie Well |
| McPhee and McGinnity Building |
| McPhee and McGinnity Paint Factory |
| Medano Ranch Headquarters |
| Meeker I.O.O.F. Lodge-Valentine Lodge No. 47 |
| Melvin School |
| Mesa Schoolhouse |
| Mesa Verde National Park |
| Metzger Farm |
| Midland Savings Building |
| Midland Terminal Railroad Depot |
| Midland Terminal Railroad Roundhouse |
Data from United States Park Service and Wikidata
