- Ohio River.100
- Ohio--Maps.2
- Old Cool Spring (Upshur County, W. Va.)1
- Old Hemlock (Preston County, W. Va.)6
- Old Man of the Canyon (W. Va.)2
- Old Muddy Creek Mill (Preston County, W. Va.)1
- Old Rock Head (Fayette County, W. Va.)1
- Old State Bridge (Marlinton, W. Va.)2
- Old Sweet Springs (Greenbrier County, W. Va.)1
- Old Sweet Springs (Sweet Springs, W. Va.)6
- Old Sweet Springs (Sweet Springs, W. Va.). Grand Hotel.1
- Old Sweet Springs (Sweet Springs, W. Va.). Jefferson Building.10
- Old Town District (New Cumberland, W. Va.)7
- Onego (W. Va.)6
- Ontario, Lake (N.Y. and Ont.)--Maps.2
- Opekiska Lock and Dam (W. Va.)4
- Opequon Creek (Va. and W. Va.)1
- Opequon Creek (Va. and W.V.)1
- Orchard Alley (Morgantown, W. Va.)1
- Organ Cave (Ronceverte, W. Va.)3