- A.J. Morrison Collection, 1754/19751
- A.P. Woodward Records, 1886/19072
- A.S. Hammack papers, 1864/19542
- Abner Osburn, Physician, Papers, 1846/19011
- Abolitionist Movement Collection, 1834/18881
- Abraham Lincoln Collection, 1860/19651
- Account Books, 1782/18952
- Account Ledger and Diary (Upstate New York), 1886/1907, bulk 1890/19002
- Accounts, 19th Century, 1836/18971
- Acker Family Diaries, 1880/19063
- Ackerly Family Papers4
- Adalbert J. Volck Collection of Etchings, 1861/19793
- Adam Empie Papers, 1811/2004, bulk 1811/18503
- Adams Brothers and Payne Building Supplies Company Ledger, 18872
- Adams Papers, 1782/18902