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 of poems, and manuscripts of lectures by Benjamin. The correspondence consists of original letters of Benjamin, typescript and photostatic copies of Benjamin letters in other libraries, and letters to Benjamin from some of his literary contemporaries including Paul Hamilton Hayne, Willis Gaylord Clark, John Lothrop Motley, and Fitz-Greene Halleck. Many of the letters relate to Park Benjamin's lecture tours. There are other family letters and many documents relating to the Benjamin family,and two letterbooks of John Lothrop Motley. Also, a large amount of genealogical material of the Benjamin family, and its related families from the 16th century to the present day. There are also financial records, monographs, clippings, and photographs.

Letters written to Gay from political and literary contemporaries such as Horace Greeley, Charles Sumner, and William Bryant; reports in letter form from his reporters at the front during the Civil War; and personal correspondence including many letters from his wife, Elizabeth Neall Gay. Letters written to Mrs. Gay from family friends and business associates including many from her husband. Correspondence of other members of the Gay family including Walter Gay, Sarah Gay, and Allan Gay. Diaries, notebooks, and journals of Sydney Howard Gay.