Correspondence, research notes, notebooks, scrapbooks, and other papers relating chiefly to Nicolay's public career particularly his tenure as secretary to President Abraham Lincoln and to his numerous literary activities including his works on Lincoln. Also documents his service as U.S. consul, Paris, France; and U.S. Supreme Court marshal. Includes papers of his daughter, Helen Nicolay. Correspondents include John Bigelow, Simon Cameron, Schuyler Colfax, William Dennison, John A. Dix, James Harlan, O.M. Hatch, John Hay, Robert Todd Lincoln, Alexander K. McClure, Charles H. Philbrick, A.C. Woolfolk, and Nicolay's wife, Therena Bates Nicolay.