Original manuscripts, 1780-1791, of the elder William Clark. Most pertain to his service in the Illinois Regiment, his administration of the Illinois grant, and the development of the towns of Clarksville on the Mississippi River near Fort Jefferson in Kentucky and of Clarksville on the Ohio River in Indiana.

Numerous letters, 1782-1790, from John Girault in New Orleans and Natchez discuss economic conditions and relations with the Spanish in the lower Mississippi River Valley. Other correspondents include his father Benjamin Clark, Richard C. Anderson, John Armstrong, Philip Barbour, James Berwick, Daniel Brodhead, Richard Ruder, Abraham Chaplin, Valentine T. Dalton, John Dodge, John Edwards, James Harrod, Gilbert Imlay, Harry limes, John Montgomery, John Rogers, Arthur St. Clair, Robert Todd, John Williams, and John Wyllys.

Among signers of military and land records are Isaiah Boone, Richard Butler, George Rogers Clark, Worden Pope, Winthrop Sargent, and James Wilkinson. These documents include muster rolls, inventories of supplies, and lists of claimants and assignees to lots in Clark's grant.