All - Constructed - 1920–1929
| Nicholson, Grace, Building |
| Nieman, Edwin J., Sr., House |
| Ninth Street Bridge |
| Nissen Building (Boundary Increase) |
| Norbeck, Peter, Summer House |
| Nordfeldt, B. J. O. and Margaret Doolittle, House |
| Norman Film Studios |
| Norris Museum/Norris Comfort Station |
| North Broad Street Station, Reading Company |
| North Dakota Mill and Elevator |
| Northern Pacific Depot |
| North Fork Solomon River Lattice Truss Bridge |
| North High School |
| North Hollywood Branch |
| North Little Rock High School |
| North Monmouth Library |
| North Topeka Baptist Church |
| Norton, Charles H., House |
| Norwood Hills Country Club |
| Norwood Memorial Municipal Building |
| Notre Dame Academy and Convent |
| Notre Dame College of Ohio |
| Oak Hall |
| Oak Hill High School |
| Oakland Park Elementary School |
| Oak Lawn Farm Dairy Barn |
| Oakton Gables |
| Ocean Parkway Jewish Center |
| Oceanside City Hall and Fire Station |
| Odd Fellows Building |
| Oglebay Mansion Museum |
| Ohio Stadium |
| Ohio Theatre |
| Ojo Caliente Hot Springs Round Barn |
| Oklahoma City Discovery Well |
| Old Collier County Courthouse |
| Old Governor's Mansion |
| Old Greenwood High School |
| Old Main, Pembroke State University |
| Old Palmetto Hotel |
| Old Port Columbus Airport Control Tower |
| Olds Hall |
| Old West Haven High School |
| Oliver, David P., High School |
| Oljato Trading Post |
| Olympia Theater and Office Building |
| Olympic Hotel |
| Omega Chapter of the Chi Phi Fraternity |
| O'Neil's Department Store |
| Open Air School |
| Orange City Colored School |
| Orchard Beach State Park |
| Oregon Caves Historic District (Boundary Increase) |
| Oregon High School |
| Orlando Apartments |
| Orpheum Theater |
| Orpheum Theater |
| Orpheum Theater and Office Building |
| Orpheum Theatre |
| Orth, Phillip, Boathouse |
| Orton Memorial Laboratory |
| Osage County Courthouse |
| Osceola Apartment Hotel |
| O'Shaughnessy Dam and Bridge |
| Oshkosh Water Tower |
| Otter Tail County Courthouse |
| Ouachita Parish High School |
| Out of Door School |
| Overbrook High School |
| Overton Hygienic Building |
| Owls Head |
| Ozark Trails Marker at Lake Arthur |
| Pacific Biological Laboratories |
| Packard, James Ward, House |
| Padre Nazario School |
| Palace Theater |
| Palace Theater |
| Palais Royale Building |
| Palmer, Edward Albert, Memorial Chapel and Autry House |
| Palmolive Building |
| Palms, Francis, Building & State Theater |
| Pan Motor Company Office and Sheet Metal Works |
| Paramount Studios Complex |
| Paramount Theatre |
| Parker, Dwight T., Public Library |
| Park Headquarters, Lassen Volcanic National Park |
| Parkhurst Building |
| Parmley, J. W., House |
| Pasadena Playhouse |
| Pascagoula Central Fire Station No. 1 |
| Paterson, J. E., House |
| Patterson, Stanley, Hall |
| Pawnee River Tributary Bridge |
| Payne, A.A.-Christo, John Sr., House |
| Peabody Hotel |
| Peace Arch |
| Peach Springs Trading Post |
| Peake High School |
| Pecos River Bridge at Terrero |
| Peery's Egyptian Theatre |
Data from United States Park Service and Wikidata
