Jasper Yeates (1745-1817) was a lawyer and Pennsylvania Supreme Court justice, one of the state's most successful colonial-era legal practitioners. After moving to Lancaster County in 1765, he became active in colonial and early federal affairs, first by supporting the Revolutionary struggle and later by serving as one of Lancaster's delegates to the State Convention of 1787, which ratified the U.S. Constitution. The Jasper Yeates Papers (1728-1910, bulk 1760-1816) consist mainly of correspondence and business and court/legal records related to the Yeates family. The bulk of this three linear foot collection reflect Yeates' personal life as husband, father, son, and friend, as well as his professional life as lawyer and judge in Pennsylvania; much of the material dated after Yeates' death was created by children and/or grandchildren.

A pioneer in ethnographic and linguistic studies of the American Indian and one of the most active members of the American Philosophical Society, Peter Stephen Du Ponceau helped to establish the American Philosophical Society's reputation as one of the world's foremost centers for the study of American Indians and their languages. The Peter Stephen Du Ponceau collection consists of correspondence on legal matters, Indian linguistics, silk culture, maritime law, the American Philosophical Society, and various publications of the early nineteenth century. The collection also includes several essays by Du Ponceau, most of which deal with maritime law.