- Office of Alumni Engagement records1
- Office of the Bursar Records, 1739/19878
- Office of the President Timothy J. Sullivan records, 1992/2005, bulk 1992/20051
- Office of the President. James Blair Records, 1695/17471
- Office of the President. James Madison Records, 1775/1979, bulk 1776/18112
- Ogden Family Papers, 1791/19462
- Ohio County (W. Va.) Court Records and Miscellaneous Papers, 1772/1954, bulk 1777/193064
- Ohio Historical Papers, 1776/18721
- Oliver Perry Chitwood, Compiler, Research Notes about and Copies of Letters by John Tyler, 1793/18621
- Ollen Lawrence Burnette, Jr. papers, 1815/20142
- Ollinger Crenshaw Papers, 1770/19703
- Orum, Eskey, and McCaffery Family Papers, 1746/20181
- Oscar Doane Lambert, Historian, Papers regarding Historical Research, 1770/19291
- Oscar Shewmake Autograph Collection, 1766/18132
- Overton family papers, 1727/1961, bulk 1781/187536