The papers of Ethan Allen Hitchcock (1798-1870) span the years 1793-1888, with the bulk of the material dating between 1830 and 1865. The papers are in English and are organized into five series: General Correspondence , Speech, Article, and Book File , Subject File , Miscellany , and Oversize .

The General Correspondence series includes letters, originals and copies, sent and received by Hitchcock primarily during his long military career. The letters describe events at the United States Military Academy in West Point, New York, and at his other posts in Florida, Mexico, and California, as well as his War Department experience during and after the Civil War. Information concerning Hitchcock’s property in St. Louis and San Francisco may be gleaned from his correspondence with his business agents, one of whom was William T. Sherman. A large part of the correspondence deals with his interest in metaphysics and philosophy which led to a pursuit of the study of alchemy and hermetic philosophy. Principal correspondents include members of the family and the many military and political figures with whom Hitchcock came into contact during his career, including William Greenleaf Elliot, William Jenkins Worth, Samuel Hitchcock, Henry Hitchcock, Mary Tyler Peabody Mann, Charles M. Hitchcock (no relation), Ethan Allen Hitchcock (nephew), George W. Cullum, Charles H. Larnard, William Wallace Smith Bliss, John Bell, and James Miller, along with some letters from Theodore Parker, Francis Lieber, and Winfield Scott.

The Speech, Article, and Book File contains Hitchcock's writings, including notes and drafts, pertaining to alchemy and hermetic philosophy. The reference notes contain not only Hitchcock’s own scholarship, but that of his brother Samuel Hitchcock and various friends. These items are supplemented by various volumes annotated by Hitchcock.

The Subject File includes correspondence, financial records, and notes chiefly from the Civil War period. Additionally, there is a manuscript entitled “The paternity of Abraham Lincoln” by William Henry Herndon and three letters about Lincoln from Herndon to Joseph Smith Fowler dated between 1887 and 1888.

The Miscellany series contains Samuel Hitchcock's diaries, alchemical and occult manuscripts from Ethen Allen Hitchcock's library, newspaper clippings, and printed matter. An Oversize series consists of appointments and commissions signed by George Washington, John Adams, John C. Calhoun, John Marshall, James Monroe, Thomas Jefferson, and others. These autographs are supplemented by several Abraham Lincoln endorsements included in the General Correspondence .