The collection consists of correspondence, documents, pamphlets, and other miscellaneous material of Sidney Clay and his family, as well as some correspondence of the Reed family. There is correspondence between Sidney Clay and his father, General Green Clay, and his mother, Sally Clay, written while he was a student at St. Thomas's College in Springfield, N.Y., (1817), and at Princeton (1818-1820), as well as correspondence with his brothers and sister Cassius, Brutus, and Paulina, and his famous cousin, Henry Clay. There are letters of Sidney Clay written in Kentucky to his second wife, Isabella Reed Clay, as well as Reed family letters. Also included in the collection are wills and correspondence with other relatives and friends. In addition, there are typescripts of a large number of the original letters and a typescript containing selections from Sidney Clay's correspondence with editorial comments by his great grandson, Clay Judson. There is a letter from Henry Clay to General Green requesting a letter of recommendation for Clay's son to be given to Rev. John Witherspoon at the College of New Jersey (now Princeton University.) Another letter is to Albert Baldwin Dod, a professor at the College of New Jersey, with an introductory letter for Clay's son. Other correspondents of Henry Clay include J. D. Hammond, J. G. Rowland, and John Scott.

Among the documents are 1818 circulars of Harvard and Princeton, describing the respective courses of study and expenses at these educational institutions, and a large broadside (1818) catalog of the officers and students of Princeton on which someone (Clay?) has identified the members of the Whig and Cliosophic Societies.