Colorado - Area of significance: Architecture
| Lancaster, James A., Site |
| Land's End Observatory |
| Lang, William, Townhouse |
| Larimer Square |
| LaSalla House |
| Las Animas Post Office |
| Las Feminilas Concilio #6 |
| Lathrop, J. V., House |
| Latuda, Frank, House |
| Laurel School Historic District |
| La Veta Pass Narrow Gauge Railroad Depot |
| La Vista Motel |
| Lay School |
| Leadville Historic District |
| Leadville National Fish Hatchery |
| Lebanon School |
| Leeman Auto Company Building |
| LeFevre, Owen E., House |
| Leiffer House |
| Lennox House |
| Lett Hotel |
| Lewis, A. T., New Building |
| Limon Railroad Depot |
| Lincoln School |
| Lincoln School |
| Lincoln School |
| Lindley-Johnson-Vanderhoof House |
| Little Buckaroo Ranch Barn |
| Little Church in the Pines |
| Little Estate |
| Littlejohn Mine Complex |
| Little Park |
| Littleton Creamery-Beatrice Foods Cold Storage Warehouse |
| Littleton Main Street |
| Littleton Post Office |
| Littleton Town Hall |
| Livermore Hotel and General Store |
| Livestock Exchange Building |
| Logan County Courthouse |
| Loma Community Hall |
| Longhurst Lodge |
| Longmont Carnegie Library |
| Longmont College |
| Lookout Mountain Park |
| Loretto Heights Academy |
| Loretto Heights Academy |
| Lorraine Lodge |
| Lost Canyon Archeological District |
| Lost Trail Station |
| Loveland State Amory |
| Lowry Field Brick Barracks |
| Luft, Conrad, Sr., House |
| Lyons Sandstone Buildings |
| Macedonia Baptist Church |
| MacGregor Ranch |
| Machebeuf Hall |
| Main Avenue Historic District |
| Maitland Estate |
| Mancos High School |
| Mancos Opera House |
| Manhattan Hotel |
| Manitou Bathhouse |
| Manitou Experimental Forest Station |
| Manitou Springs Historic District |
| Manzanola United Methodist Church (MUMC) |
| Marble City State Bank Building |
| Marble High School |
| Marble Jailhouse |
| Marble Town Hall |
| Margery Building |
| Martin Mining Complex |
| Masonic Temple Building |
| Matchless Mine |
| Mathews House |
| Maxwell Building |
| Maxwell Park School |
| Maxwell, R. G., House |
| Maysville School |
| Maytag Aircraft Building |
| McAllister House |
| McClelland Orphanage |
| McClellan House |
| McClintock Building |
| McClure House |
| McCormick House |
| McCourt, Peter, House |
| McCreery, William H., House |
| McFadden Barn |
| McFadden Brothers Ranch East Headquarters |
| McGraw Ranch |
| McGregor Hall |
| McHugh-Andrews House |
| McIntire Ranch |
| McPhee and McGinnity Building |
| McPhee and McGinnity Paint Factory |
| Mechanics Building/Masonic Building |
| Medano Ranch Headquarters |
| Meeker I.O.O.F. Lodge-Valentine Lodge No. 47 |
| Melvin School |
| Mesa Schoolhouse |
Data from United States Park Service and Wikidata
