Places
- Oakland (Md.)1
- Ohio12
- Ohio -- History1
- Ohio County (W. Va.)11
- Ohio River8
- Ohio River Valley3
- Ohio River Valley -- History1
- Ohio River and Valley.3
- Old Point Comfort (Va.)--History--19th century1
- Opekiska (W. Va.)1
- Orange County (Va.) -- History1
- Oregon -- History -- 1859-1
- Oregon -- History -- To 18591
- Oxford (Miss.)1