The Honorable James H. Duncan papers are comprised of materials relating to Duncan's personal affairs, legal affairs and business activities in the first half of the nineteenth century. The bulk of the material is from 1668 to 1910. This collection has been divided into three series.

Series I. Personal Papers includes correspondence, estate papers, receipts, and printed matter. The personal correspondence consists of letters received from family members and friends. The civic and societal correspondence contains items concerning Duncan's activities as a member of the Brown University Board of Fellows, the American Baptist Missionary Union, and the Essex Agricultural Society.

Series II. Professional and Business Papers has been divided into two subseries. Subseries A. Political Papers is largely comprised of letters received from mentors John Varnum and Leverett Saltonstall. Many of the letters from 1819 and the early 1850s document the concerns of local residents on the issues of slavery and secession. The Whig Convention papers illustrate the election of delegates from twenty-one Essex County townships to a convention of National Republicans (Whigs) held in Ipswich, Massachusetts in 1831. Subseries B. Legal and Business Papers document the close relationship between Duncan's legal work as a probate lawyer and Justice of the Peace and his real estate investments in eastern Massachusetts and New Hampshire. The correspondence contains information on Duncan's management of various real estate transactions, as well as material concerning the Boston and Maine railroad. The real estate transactions are largely deeds and agreements in which Duncan conducted business for himself or on behalf of clients. The papers of the Haverhill Bridge document the activities of the proprietors of the bridge and associated land transactions and disputes. The railroad corporation materials contain notes on the status of a number of railroads, including the Haverhill and Andover, Eastern, Western, and the Andover and Wilmington lines. The Eliphalet Webster account papers are financial statements for a store owned by Duncan and managed by Webster.

Series III. Duncan Family Papers includes papers from a number of Duncan's family members. This series has been divided into two subseries. Subseries A. James Duncan Sr. and James Duncan Jr. Papers contains mostly probate items concerning related land transactions. The Samuel White estate was managed by his son-in-law, James Duncan, Jr. These probate records are remarkably complete and involve a large number of real estate transactions. Subseries B. James H. Duncan Family Papers contain items associated with Duncan's wife, Mary (Willis) Duncan, her father Benjamin Willis, and three of Duncan's children; the majority of the papers are personal letters between family members. The Benjamin Willis correspondence is comprised of letters from his son William during a voyage on the schooner Union. Of particular interest are the papers of Mary (Duncan) Harris, who was interested in the work of Baptist missionaries in Japan and Turkey. Rebecca Duncan's autograph book contains notes and signatures from a number of nationally prominent individuals such as Thomas Hart Benton, Andrew Johnson, Thaddeus Stevens, Winfield Scott, Millard Fillmore, and Daniel Webster.