- A.S. Hammack papers, 1864/19542
- Abner Osburn, Physician, Papers, 1846/19011
- 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, 1880/19065
- Ackerly Family Papers4
- Adalbert J. Volck Collection of Etchings, 1861/19794
- Adam Empie Papers, 1811/2004, bulk 1811/18503
- Adam Finch Collection, 1891/19332
- Addison Family Papers, 1890/18992
- Adele Goodman Clark papers, 1849/19784
- Adin B. Underwood Papers, 1861/19262
- Administration records collection, 1776/197622