Series III. Family Papers, 1638-1936, covers a wide variety of individuals. Nathan Endicott's (1790-1858) shipping letterbook reflects his career as a shipping merchant trading with London, Leningrad, and St. Thomas. Samuel Endicott Jr.'s (1795-1828) shipping account book contains accounts with Joseph and Joseph A. Peabody, and accounts of the ships Catherine and Augustus' voyages to Antwerp, Hamburg, Leningrad, Helsingor, Marseilles, Djakarta, Havana, and Charleston, South Carolina.

William Crowninshield Endicott's (1826-1900) papers contain correspondence and accounts documenting his roles as attorney and Secretary of War. His correspondence includes letters written as Secretary of War concerning Crow Indians. William's account books contain guardianship, trustee's or attorney's accounts for Dudley P., George W., and Eliza P. Rogers, J. Watson Andrews, Charles Endicott, and Jacob C. Rogers.

The miscellaneous family papers include correspondence and financial papers of Samuel, Robert, Henry, John, George W., E.M., Lewis, William P., and William Crowninshield Endicott Jr. William Crowninshield Endicott Jr.'s letters include various historical memorials and celebrations, and his resignation of the Essex Institute presidency. Of note are legal documents of Governor John Endecott: a copy of a 1638 agreement and an original notarized agreement of 1653.