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.

Three volumes contain letters, laws, charters, reports, proclamations, petitions, and other official and semi-official documents relating principally to early Pennsylvania and New Jersey, signed by or addressed to William Penn, among others. A fourth volume is Penn's cash book, 1699-1703, which records expeditures, payments of quit rents, etc. Tipped in is "Catalogue of Goods left at Pensbury," and of goods left at Philadelphia, 1701.

The first volume includes extracts from the journals of Conrad Weiser and Christian Frederick Post (1757), Charles Thomson's "An Enquiry into the causes of the alienation of the Delaware and Shawanese Indians from the British interest" (1759), and a printed version of Judge Bradford's "Statement of facts and observations respecting the penal laws" (1792). The second volume contains selected letters and documents in the Pennsylvania state records on Indian relations, including transcriptions of several treaties between the Province of Pennsylvania and the Delawares and other Indians (1755-1758); the French and Indian War; and Braddock's campaign. Some manuscripts are written by Deborah Norris Logan and Charles Thomson.