Correspondence, manuscripts, memoranda, receipts, certificates, financial and legal documents, envelopes, clippings, pamphlets, and other printed materials dealing with social and family relationships, the sons' education, professions, and military careers, the Mexican-American War and the Civil War, real estate and financial matters, and with the deaths and bequests of various family members. Among the cataloged correspondents are: Alexander Hamilton, John Church Hamilton, Gen. Schuyler Hamilton, Ralph Isaacs Ingersoll, Charles Augustus Peabody, Gen. J. Fred Pierson, Gen. Winfield Scott, Martin Van Buren, and a manuscript by George Washington.

Correspondence, manuscripts, notes, memoranda, notebooks, notecards, proofs, photographs, microfilms, and printed materials. The Papers include the manuscript research materials and correspondence for each of his books except his biography of Theodore Dreiser. Among the correspondents are William Benton, Bruce Catton, Carey McWilliams, Mrs. Fremont Older (Cora Miranda Baggerly Older), and Thornton Wilder.