- O'Shaughnessy Family Papers, 1857/196512
- O. D. Lambert Research Notes and Biographical Material on Stephen B. Elkins, 1888/19061
- O.D. Linder, Compiler, Genealogy Records Regarding the Boyce, Dever, Gibson, and Linder Families, 1860/2000, bulk 1900/20001
- O.P. Sydenstricker Prescription Books, 1884/18941
- Oak Grove Baptist Church Records, 1853/19591
- Octavius Hileman Papers, 1890/18992
- Office of Admission records, 1861/20213
- Office of Alumni Engagement records1
- Office of Communications and Marketing subject files, 19506
- Office of the Bursar Records, 1739/19873
- Office of the Dean of the School of Law - Record Group 81
- Office of the President Timothy J. Sullivan records, 1992/2005, bulk 1992/20051
- Office of the President, John Augustine Smith Records, 1814/1944, bulk 1814/18262
- Office of the President. Benjamin Stoddert Ewell records, 1848/1898, bulk 1866/18862
- Office of the President. James Blair Records, 1695/17471