Places
- Oakland (Md.)1
- Ohio12
- Ohio -- Civil War, 1861-18651
- Ohio -- History1
- Ohio County (W. Va.)8
- Ohio River10
- Ohio River Valley5
- Ohio River Valley -- History2
- Ohio River and Valley.2
- Olympia, W.A.1
- Opekiska (W. Va.)1
- Orange County (Va.)1
- Orange County (Va.) -- History1
- Oregon -- History -- 1859-1
- Oregon -- History -- To 18591