All - Constructed - 1910–1919
| Mountain Quarries Bridge |
| Mountain States Telephone and Telegraph Company |
| Mount Beulah Hotel |
| Mount Horeb Public School |
| Mount Pleasant Carnegie Library |
| Mount Saint Michael |
| Mount Tamalpais Mountain Theater |
| Mount Theodore Roosevelt Monument |
| Mount Tremper Fire Observation Station |
| Mt. Hood Hotel Annex |
| Mt. Mercy Academy and Convent |
| Mt. Pleasant School |
| Mudbaden Sulphur Springs Company |
| Mueller Bridge |
| Muirdale Tuberculosis Sanatorium |
| Municipal Auditorium |
| Municipal Building |
| Municipal Building |
| Municipal Building |
| Munson-Williams-Proctor Arts Institute |
| Murphy Farms Number 1 |
| Murphysboro Elks Lodge |
| Murphy Trail and Bridge |
| Music Pavilion |
| Myers and Gross Building |
| Nahma and Northern Railway Locomotive #5 |
| NASA Langley Research Center (LaRC) Historic District |
| Nashold 20-sided Barn |
| National Biscuit Company Building |
| National Cathedral, The |
| National State Bank |
| Natural History Museum |
| Naval Air Station, San Diego, Historic District |
| Naval Military Hangar-University Shell House |
| Nave Apartments |
| Neessen, Chris, House |
| Neitzel, H. R., House |
| Nelson Cemetery Walk |
| Nevada-California-Oregon Railroad Depot |
| Newberry, J. J., Company |
| New Cliff House |
| New Effington Hospital |
| New Lawn, The |
| New Orleans and Northeastern Railroad Depot |
| New Richmond News Building |
| New Salem Covered Bridge |
| New York Amsterdam News Building |
| New York, The |
| Nichols, Harry H., House |
| Nixon, Richard, Birthplace |
| Nohlechek, Rhoda, House |
| Noon, A. S., Building |
| Norby House |
| Norris Ford Covered Bridge |
| Northbrook Lodge |
| Northern Pacific Passenger Depot |
| North Hall-River Falls State Normal School |
| North La Junta School |
| Northland |
| North Loup Bridge |
| North Manchester Public Library |
| North Watervliet Road-Paw Paw Lake Outlet Bridge |
| Northwestern National Bank Building |
| North Woodward Congregational Church |
| Norwood Municipal Building |
| Notre Dame Catholic Church |
| Noves, Charles W., House |
| Nymore Bridge |
| Oak Creek Dam |
| Oakland City Hall |
| Oakley, Annie, House |
| Oak Ridge Apartments |
| Occidental Life Building |
| Ocean City City Hall |
| O'Connell, Clara T., School |
| Odd Fellows Building and Auditorium |
| Odd Fellows Cemetery |
| Odd Fellows Home of Dell Rapids |
| Oheka |
| Ohio Moline Plow Company Building |
| Ohio State Normal College At Kent |
| Ohio State Reformatory |
| Oklahoma City Ford Motor Company Assembly Plant |
| Oklahoma, New Mexico and Pacific Railroad Depot |
| Oklahoma State Capitol |
| Old Armijo School |
| Old Benton-Sardis Road Bridge |
| Old Bnai Zion Synagogue |
| Old District 10 Schoolhouse |
| Old Hattiesburg High School |
| Old Ladore School |
| Old Nogales City Hall and Fire Station |
| Old Ohio Union |
| Old Post Office |
| Old Rockport Hutterite Colony |
| Old Tower Two |
| Old US Post Office and Courthouse |
| Oliver Building |
| Olson, August, House |
| Omaha High School |
Data from United States Park Service and Wikidata
