Original papers, 1791-1817, of both uncle and nephew. Only a few, however, are those of the elder Symmes. Included are three letters (1791, 1800) to Governor Arthur St. Clair of the Northwest Territory, detailing political and judicial differences between the two men, and one letter (1811) to James Henry discussing the burning of Symmes's house, a Fourth of July celebration in Cincinnati, and immigration to the Miami Purchase area.

The bulk of the papers are those of the younger Symmes. Among his military papers are contemporary copies of two orders (1803, 1804) by James Wilkinson. Extensive personal correspondence (1802-1817) was exchanged between Symmes and his brothers Daniel and Peyton, his wife Marianne, his mother Mercy, his uncle, and other family members. Within some letters are discussions of life in Cincinnati and on frontier military posts in both war and peace, particularly Bellefontaine on the Missouri River. Others pertain to the early development of his theory on the hollow construction of planets. Among other correspondents are Madeleine Askin, Ethan A. Brown, Anthony Campbell, John Campbell, E.B. Clemson, William Eustis, Willis Foulk, Thomas Hamilton, William Henry Harrison, Jacob Kingsbury, Hugh Moore, R.C. Nicholas, Charles Peltier, Horatio Stark, William Swan, and David Walker.