- O'Shaughnessy Family Papers, 1857/196516
- O. Henry Collection5
- O.D. Linder, Compiler, Genealogy Records Regarding the Boyce, Dever, Gibson, and Linder Families, 1860/2000, bulk 1900/20001
- O.J. Morrison Department Stores Company (West Virginia and Ohio) Records, 1910/1985, bulk 1940/19501
- O.W. Riegel Papers, 1900/19922
- Oak Grove Baptist Church Records, 1853/19591
- Office of Admission records, 1861/20214
- Office of Alumni Engagement records3
- Office of Communications and Marketing subject files, 195017
- Office of University Development records1
- 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, 1992/20051
- Office of the President, John Augustine Smith Records, 1814/1944, bulk 1814/18262
- Office of the President. James Blair Records, 1695/17471