All - Architectural style - Renaissance Revival architecture
| Northwestern Hotel |
| North Wheeling Historic District |
| Notre Dame Academy and Convent |
| Nottoway Plantation House |
| Nugent Home for Baptists |
| Nuits |
| Null House |
| Nye County Courthouse |
| Oakes, J. J., House |
| Oak Hill Park Historic District |
| Oakhurst |
| Oakland Hotel |
| Oakland YWCA Building |
| Oakleigh Garden Historic District (Boundary Decrease & Additional Documentation) |
| Oakley |
| Oaks, The |
| Oberlin Lake Shore And Michigan Southern Station |
| O'Brien General Store and Post Office |
| O'Connor, Cornelius, House |
| O'Connor, Thomas M., House |
| Odd Fellows Building |
| Odd Fellows Building |
| Odd Fellows Hall |
| Odd Fellows Hall |
| Odd Fellows Hall |
| Odd Fellows Hall |
| Odd Fellows' Home for Orphans, Indigent and Aged |
| Odd Fellows Home of Dell Rapids |
| Odd Fellows Temple |
| O'Hara, John, House |
| Oil City Downtown Commercial Historic District |
| Oil City North Side Historic District |
| Oil City South Side Historic District |
| Oklahoma State Capitol |
| Okolona |
| Old Asbury Methodist Church |
| Old Bartow County Courthouse |
| Old Biology Hall |
| Old Chestnut Hill Historic District |
| Old Christiansburg Industrial Institute |
| Old City Historic District |
| Old Customhouse |
| Old Downtown Harrisburg Commercial Historic District |
| Old Federal Building and Post Office |
| Oldfields |
| Old Hoosier Theatre |
| Old Indiana County Jail and Sheriff's Office |
| Old Iroquois County Courthouse |
| Old Jefferson Parish Courthouse |
| Old Laclede Gas and Light Company Building |
| Old Lehigh County Courthouse |
| Old Logan County Courthouse |
| Old Madison County Courthouse |
| Old Main, Augustana College |
| Old Main Street Historic District |
| Old Main, Western Washington State College |
| Old Mauch Chunk Historic District |
| Old McHenry County Courthouse |
| Old Medford High School |
| Old Naval Hospital |
| Old New England Building |
| Old Post Office |
| Old Post Office |
| Old Post Office Building |
| Old Post Office Building |
| Old Post Office Building and Customhouse |
| Old Pottstown Historic District |
| Old Railroad Savings and Loan Building |
| Old Rockville High School and East School |
| Old Sedgwick County Courthouse |
| Old State Mutual Building |
| Old Third District Courthouse |
| Old Uptown Harrisburg Historic District |
| Old U.S. Courthouse and Post Office |
| Old Watson Homestead House |
| Old Worth County Courthouse |
| Omaha Public Library |
| Open Air School |
| Opera Hall Block |
| Oquirrh School |
| Orange Commercial Historic District |
| Orange County Courthouse |
| Orange Station |
| Orange Street Historic District |
| Oregon Mill Complex |
| Orendorff, John, Farm |
| Oriental Building Association No. 6 Building |
| Orient Historic District |
| Orleans County Courthouse Historic District |
| Orpheum Theatre |
| O'Shea Building |
| Oskaloosa City Hall |
| Oskaloosa City Square Commercial Historic District |
| Oskaloosa Fire Station |
| Ostheimer, Martha and Maurice, Estate |
| Oswego-Oneida Streets Historic District |
| Ottendorfer Public Library and Stuyvesant Polyclinic Hospital |
| Ottumwa Young Women's Christian Association |
| Oulagisket |
| Overackers Corners Schoolhouse |
Data from United States Park Service and Wikidata
