Colorado - Area of significance: Architecture
| Mesa Verde Administrative District |
| Mesa Verde National Park |
| Methodist Episcopal Church |
| Methodist Episcopal Church of Montrose |
| Metzger Farm |
| Midland Savings Building |
| Midland Terminal Railroad Depot |
| Midway House |
| Millage Farm Rural Historic District |
| Mill City House |
| Milne Farm |
| Milner Pass Road Camp Mess Hall and House |
| Milner-Schwarz House |
| Mingus Homestead |
| Minnequa Steel Works Office Building and Dispensary, Colorado Fuel and Iron Company |
| Minnie Gulch Cabins |
| Mint Saloon |
| Miramont |
| Missouri Heights School |
| Mitchell Springs Archeological Site |
| Modoc Mill |
| Monte Vista Downtown Historic District |
| Monte Vista Library |
| Montezuma Schoolhouse |
| Montezuma Valley National Bank and Store Building |
| Montgomery Court |
| Montgomery Hall, Colorado College |
| Montgomery Ward Building |
| Montoya Ranch |
| Montrose City Hall |
| Montrose County Courthouse |
| Montrose Fruit & Produce Association Building |
| Montrose Masonic Temple, Lodge No. 63 |
| Montview Boulevard Presbyterian Church |
| Monument Lake Park Building and Hatchery Complex |
| Monument Valley Park |
| Moore, Dora, Elementary School |
| Morgan County Courthouse and Jail |
| Mosman House |
| Mosque of the El Jebel Shrine |
| Mountainside Lodge |
| Mount Saint Scholastica Academy, East Building |
| Mount St. Gertrude Academy |
| Mount Vernon House |
| Mt. Pleasant School |
| Nachtrieb-Kelly Ranch |
| National Hotel-Wolff Building |
| Navajo Hogan |
| Neef, Frederick W., House |
| Nettleton-Mead House |
| Neusteter Building |
| Newberry House |
| New Brick-The Brick Saloon |
| Newman Block |
| New Terrace |
| Nichols House |
| Nordlund House |
| Norlin Quadrangle Historic District |
| Norman Apartments |
| North End Historic District |
| North La Junta School |
| North Seventh Street Historic Residential District |
| North Weber Street-Wahsatch Avenue Historic Residential District |
| Notch Mountain Shelter |
| Nunns, John Herbert, House |
| Nurses' Home |
| Ochsner Hospital |
| Office of Civil Defense Emergency Operations Center |
| Ogden Theatre |
| Old Colorado City Historic Commercial District |
| Old Highland Business District |
| Old Livery Stable |
| Old Town Fort Collins |
| Oltjenbruns Farm |
| Opera House Block/Central Block Building |
| Oriental Theater |
| Orman-Adams House |
| Osgood Castle |
| Osgood Gamekeeper's Lodge |
| Osgood-Kuhnhausen House |
| Ouray City Hall and Walsh Library |
| Ouray Historic District |
| Our Lady of Guadalupe Church |
| Our Lady of Guadalupe Church and Medina Cemetery |
| Our Lady of Mount Carmel Church |
| Overland Cotton Mill |
| Owen Estate |
| Oxford Hotel |
| Oxford Hotel |
| Pacific Express Stable |
| Painted Hand Pueblo |
| Palace Hotel |
| Palmer Hall |
| Palmer, Judge Peter L. House |
| Paonia First Christian Church |
| Paramount Theater |
| Parish, Harvey J., House |
| Paris Mill |
| Park County Courthouse and Jail |
| Park Hill |
Data from United States Park Service and Wikidata
