- Oarr, Dwight1
- Old Bay State Course1
- Old Soldier (fl. 1865)1
- Olshansky, Ludwig1
- Orangeburg Bar1
- Oratorio Society of New York1
- Orcutt, L., 1830-1
- Orr, J. L. (James Lawrence), 1822-18731
- Orshansky, Mollie1
- Osborn, Alex F. (Alex Faickney)1
- Ott, Oliver Frank, 1866-19391
- Paderewski Birthday Celebration1
- Paderewski Foundation1
- Palmer, B. M. (Benjamin Morgan), 1818-19021
- Palmer, Benjamin M. (Benjamin Morgan), 1781-18471
- Pappastavrou, George1
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- Pemberton, A. H.1