Texas - Criteria: C (architecture/engineering)
| Novy, Joe, House |
| Nueces County Courthouse |
| Nuestra Senora del Espiritu Santo de Zuniga Site |
| Nuggett Hill Historic District |
| Number 4 Hook and Ladder Company |
| Oakes Hotel Building |
| Oakhurst Historic District |
| Oak Lawn Methodist Episcopal Church, South |
| Oakwood Cemetery Annex |
| Oakwood Cemetery Historic District |
| Oblate Park Historic district |
| O'Bryne, John and Eva, House |
| O'Connor-Proctor Building |
| O'Connor, Thomas M., House |
| Ogle, Joseph, House |
| Oil Springs Oil Field Discovery Well |
| Old Alton Bridge |
| Old Beer and Ice Warehouse |
| Old Bnai Zion Synagogue |
| Old Brazoria County Courthouse |
| Old Brownson School |
| Old Brulay Plantation |
| Old Bryant-Link Building |
| Old Continental State Bank |
| Old Federal Building and Post Office |
| Old Federal Building-Federal Courthouse |
| Old Frio County Jail |
| Old Galveston Customhouse |
| Old Georgetown High School |
| Oldham Avenue Historic District |
| Oldham, Mary and Frank House |
| Old Hidalgo Courthouse and Buildings |
| Old Hidalgo School |
| Old Houston National Bank |
| Old Land Office Building |
| Old Lone Star Brewery |
| Old McCulloch County Jail |
| Old Mercantile Building |
| Old Morris County Courthouse |
| Old Municipal Assembly Hall |
| Old Nacogdoches University Building |
| Old Nazareth Academy |
| Old Pierce House |
| Old Reagan County Courthouse |
| Old Rock Saloon |
| Old San Francisco Historic District |
| Old Sherman Public Library |
| Old Sixth Ward Historic District |
| Old Spanish Trail from US 90 to I-10 |
| Old St. Anthony's Catholic Church |
| Old St. Luke's Episcopal Church |
| Old Town Historic District |
| Old Town Residential Historic District |
| Old U.S. Post Office and Courts Building |
| Old Victoria County Courthouse |
| Old West Austin Historic District |
| Old West Texas Utilities Company |
| Old Wooten, H. O., Grocery |
| Oliphant House |
| Oliphant-Walker House |
| Olive, L. W., House |
| Olive Street Historic District |
| Olson-Hanson Farm |
| Olson, Joseph and Anna, Farm |
| Olson-Nelson Farm |
| One Main Place |
| Onion Creek Post Office and Stagecoach House |
| Orange Show, The |
| Orgain, Elbert S., House |
| Orgain, Sarah Jane, House |
| Oriental Textile Mill |
| Original Town Residential Historic District |
| Ott, Charles J. and Alvina, House |
| Otto House |
| Ott, S. I., House |
| Our Lady of Lourdes Church |
| Our Lady of Mount Carmel and St. Therese Church |
| Our Lady of Victory Academy |
| Our Mother of Mercy Catholic Church and Parsonage |
| Oxsheer, Fountain G. and Mary, House |
| Paddock Viaduct |
| Page-Gilbert House |
| Page, Paul D., House |
| Paggi, Michael, House |
| Paige-DeCrow-Weir House |
| Paillet House |
| Palace Hotel |
| Palace Theatre |
| Palapa Table for James Richard Marmion |
| Palestine Carnegie Library |
| Palestine High School |
| Palmer, Edward Albert, Memorial Chapel and Autry House |
| Palo Pinto County Courthouse |
| Palo Pinto County Jail |
| Pampa City Hall |
| Pampell-Day House |
| Panhandle Inn |
| Panna Maria Historic District |
| Panola County Jail |
| Panther Junction Mission 66 Historic District |
Data from United States Park Service and Wikidata
