Digital collections available from the Massachusetts Historical Society including: Adams Papers Digital Edition; Thomas Jefferson Digital Collection; Coming of the American Revolution; and others.
Suggested terms to look for include - diary, diaries, letters, papers, documents, documentary or correspondence.
Combine these these terms with the event or person you are researching. (example: civil war diary)
Also search by subject for specific people and events, then scan the titles for those keywords or others such as memoirs, autobiography, report, or personal narratives.
Off campus access instructions (for e-books)
The Diary and Autobiographical Writings of Louisa Catherine Adams, 1778-1849 by 
A Traveled First Lady: Writings of Louisa Catherine Adams by 