Texas - Significance region: Local
| Odom, Addie L. and A.T., Homestead |
| Offenhauser Insurance Building |
| Ogle, Joseph, House |
| Oil & Gas Building |
| Old Alton Bridge |
| Old Bakery |
| Old Bastrop Co. Pavilion |
| Old Beer and Ice Warehouse |
| Old Bnai Zion Synagogue |
| Old Brulay Plantation |
| Old Bryant-Link Building |
| Old City Mills |
| Old Continental State Bank |
| Old Federal Building-Federal Courthouse |
| Old Frio County Jail |
| Old Georgetown High School |
| Oldham Avenue Historic District |
| Oldham, Mary and Frank House |
| Old Hidalgo School |
| Old Houston National Bank |
| Old Lyford High School |
| Old Market House Museum |
| Old Masonic Hall |
| Old McCulloch County Jail |
| Old Mercantile Building |
| Old Morris County Courthouse |
| Old Penick-Hughes Company |
| Old Post Sanitarium |
| Old Reagan County Courthouse |
| Old Rock Saloon |
| Old Sherman Public Library |
| Old Sixth Ward Historic District |
| Old St. Anthony's Catholic Church |
| Old St. Luke's Episcopal Church |
| Old Town Historic District |
| Old Town Residential Historic District |
| Old Wallisville Town Site |
| Old West Austin Historic District |
| Old West Texas Utilities Company |
| Old Wooten, H. O., Grocery |
| Oliphant-Walker House |
| Olive, L. W., House |
| Oliver, Dr. William Holt, House |
| Oliver-Eakle-Barfield Building |
| Olive Street Historic District |
| One Main Place |
| Onion Creek Post Office and Stagecoach House |
| Orgain, Elbert S., House |
| Orgain, Sarah Jane, House |
| Oriental Textile Mill |
| Original Town Residential Historic District |
| Osborn Site |
| O.S. Ranch Petroglyphs 41 GR 57 |
| Ott, Charles J. and Alvina, House |
| Otto House |
| Ott, S. I., House |
| Our Lady of Mount Carmel and St. Therese Church |
| Our Lady of Victory Academy |
| Our Mother of Mercy Catholic Church and Parsonage |
| Our Mother of Mercy School |
| Oxsheer, Fountain G. and Mary, House |
| Pagan Site, 41 LK 58 |
| Page-Gilbert House |
| Page, Paul D., House |
| Paggi, Michael, House |
| Paige-DeCrow-Weir House |
| Paillet House |
| Palace Hotel |
| Palacios Colored School |
| Palapa Table for James Richard Marmion |
| Palestine Carnegie Library |
| Palestine High School |
| Palestine New Town Commercial Historic District |
| Palmer, Edward Albert, Memorial Chapel and Autry House |
| Palmville |
| Palo Pinto County Courthouse |
| Palo Pinto County Jail |
| Pampa City Hall |
| Pampell-Day House |
| Pan-American Courts and Cafe |
| Panhandle Inn |
| Panola County Jail |
| Panther Junction Mission 66 Historic District |
| Pape-Borchers Homestead |
| Paramount Theater |
| Paramount Theatre |
| Paris Commercial Historic District |
| Parker-Bradshaw House |
| Parker-Browne Company Building |
| Parker, James F. and Susie R., House |
| Parker, John W., House |
| Parker Lumber Company Complex |
| Parker, Milton, House |
| Park Hotel |
| Parkland Apartments |
| Parkland Hospital |
| Parmer County Courthouse |
| Parque Zaragoza |
| Parramore, D. D., House |
| Parramore Historic District |
Data from United States Park Service and Wikidata
