Approximately 12,000 letters to Allan Nevins from various correspondents including James Truslow Adams, Franklin Delano Roosevelt, Harry S. Truman, Willa Cather, Frances Folsom Cleveland, Van Wyck Brooks, Robert Frost, Newton D. Baker, Archibald MacLeish, John D. Rockefeller, Jr., Carl Sandburg, and Henry Wallace; notes and typescripts for Nevins' books including Emergence of Lincoln, The Ordeal of Democracy, Rockefeller, and History and Historians, with notes by editor Ray A. Billington; miscellaneous transcripts, clippings, newspapers, and photographs. Also, autograph letters and manuscripts by presidents, Civil War figures, financiers, politicians, and authors. There are also the Brand Whitlock World War I Diaries and letters to him by such people as Herbert Hoover, Gen. John J. Pershing, and others.

Cotton's 15 nonconsecutive manuscript pocket diaries for the period from 1850 to 1877. The diaries outline his life and travels. The entries for the Civil War years are especially interesting. He often describes the capital's fear of enemy invasion, recent nearby incursions, troop movements, and the general preoccupation with all aspects of the war. He called on President Lincoln, attended his second inauguration, and notes the passage of the Emancipation Proclamation. He describes the capital's joyous mood at the fall of Richmond and the gloom over the assassination of Lincoln. He attended the military court to see the conspirators. Later volumes talk about Pension Bureau affairs and his health and that of his family.

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 files of Roberts Brothers, pertaining to all departments, editorial, production, advertising, and sales. Also, some miscellaneous letters and documents, unrelated to Roberts Brothers, which deal with various legal matters, including those of Frederick D. Ely and of William A. Dunn, from 1838 until 1932, and letters to the Secretary of Harvard University from 1900 to 1907.

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.