Oakley, John [3 subentries]

oats [3 references]

Oben, Thomas [2 subentries]

O'Brien, Richard [4 subentries]

Observations on the Cow-Pock (John Coakley Lettsom) [3 references]

“Observator” (pseudonym) [1 reference]

Océan (French ship-of-war) [1 reference]

“Ode to the Mammoth Cheese” (Thomas Kennedy) [1 reference]

Odyssey (Homer) [2 references]

Oelrichs, Arnold [1 reference]

O'Finn, Edmund [3 subentries]

Ogden, Aaron [1 reference]

Ogden, John C. [1 reference]

Ogilsby, Samuel [1 reference]

Ohio [16 subentries + 2 “see also” entries]

Ohio Company [1 reference]

Ohio River [5 references]

Oldham, James [7 subentries]

Oliver, Robert [1 reference]

O'Neale, William [1 reference]

O'Neill, Arturo [2 references]

Origin of the Vaccine Inoculation (Edward Jenner) [1 reference]

ornaments [1 subentry]

orphans [4 references]

orthography [1 reference]

Ortiz de Zugasti, Pedro [1 reference]

Osgood, Samuel [3 references]

Ostend [3 references]

Otis, Harrison Gray [3 references]

Otis, Samuel A. [5 subentries]