The incoming correspondence of Vanderpoel, containing letters from friends, clients, and colleagues and dealing with personal and legal matters. Correspondents include Henry M. Alexander, William Allen Butler, John P. and William V. S. Beekman, G. W. Bulkey, Joseph H. Choate, Frederic R. Coudert, Lewis L. Delafield, Jay Gould, William D. F. Maurice, Edward Pierpont, J. Bryce Smith, John Van Alen, John and Thomas Van Buren, and Henry Vanorden. Letters of a personal and business nature from various family members include several from Aaron and John Vanderpoel and Lewis Oakley, his uncles, and from Henry C. Van Schaack, his father-in-law. There are approximately twelve manuscripts of essays and speeches by A. J. Vanderpoel while he attended Kinderhook Academy and New York University, as well as a few by other family members. Various documents including mortgages, deeds, indentures, agreements, and court records relate to Vanderpoel's law practice and to family property.

Correspondence and legal and business papers of Peter Van Schaack and his family. The collection includes letters to and from Egbert Benson, Henry Cruger, James Duane, William Laight, Theodore Sedgwick, Peter Silvester, John Vardill, and many others. The letters deal with such subjects as taxation, the siege of Boston, George Washington, Tories, the Jay Treaty, Shays' Rebellion, and the many prominent people with whom Van Schaack was acquainted, including the Jay family and Gouverneur Morris. There is a large number of letters to and from his brother, Henry Van Schaack (1733-1823). The correspondence contains many political and social opinions regarding America and England before, during, and after the Revolutionary War. Many of the legal documents concern the disputed claims to the Van Rensselaer properties in Claverack and Westenhook, N.Y., as well as land claims around Kinderhoek, N.Y. Henry Cruger Van Schaack added to the collection more letters from well-known people as well as legal and family papers. These are mostly dated in the mid-19th century, and deal in part with the Delaware and Hudson Canal Company, the Berkshire Iron Works, and similar business ventures. Many documents are Colonial-era deeds or concern early land disputes such as the New York-Massachusetts boundary dispute.