Oak Hill (Monroe's Loudoun County, Va., estate) [1 reference]

Oates, Titus [1 reference]

Observations on the Commerce of the American States (pamphlet) [1 reference]

Occoquan, Va. [1 reference]

Ocracoke, N.C. [1 subentry]

Ogden, Samuel [1 reference]

Ogdensburg, N.Y. [2 references]

Ohio [10 references + 14 subentries]

Ohio County, Va. (now W.Va.) [1 reference]

Ohio Gazetteer [1 reference]

Ohio River [3 references]

“The Old Bachelor” (essays) [1 reference]

The Olive Branch: or, Faults on Both Sides, Federal and Democratic [3 references]

Oneida (U.S. brig) [1 reference]

Onís, Luis de [9 references + 1 subentry]

On the Origin, Nature, Progress and Influence of Consular Establishments [1 reference]

Opelousas, La. [2 references]

Orange County, N.Y. [1 reference]

Orange County, Va. [4 references]

Orange County Courthouse, Va. [1 reference]

Orders in council [See redirect]

“Original Principles” (essay) [1 reference]

Orleans, Island of [1 reference]

Orleans County, Orleans Territory [1 reference]

Orleans Territory [2 subentries]

Ormsby, Stephen [2 references]

Orphans [1 subentry]

Osage Indians [5 references + 3 “see also” entries]

Osage River [1 reference]

Osgood, David [1 reference]

Osgood, Samuel [1 reference]

Oswego, N.Y. [1 reference]

Otis, Harrison Gray [3 references + 1 subentry]

Ott, David [See redirect]

Ott, John [1 reference + 1 subentry]

Ottawa Indians [2 references]

Ottawa River [2 references]

Ovid [1 reference]