The Hassam Family Papers consists of correspondence, diaries, scrapbooks, receipts, memorabilia, genealogy, and more. It has been arranged into five series: Series I. John Tyler Hassam Papers; Series II. Nelly Alden Batchelder Hassam Papers; Series III. Eleanor Hassam Papers; Series IV. John Henry Batchelder Papers; and Series V. Hassam Family Members' Papers.

Series I. John Tyler Hassam Papers has been arranged into five subseries: Personal Papers; Law Practice Records; Genealogical Research; Military Records; and Financial Records. Subseries A. Personal Papers contains personal letters to John T. Hassam, legal papers, and a diary he wrote while visiting Europe in 1873-1874. Subseries B. Law Practice Records contains correspondence and papers relating to his legal practice and Suffolk County (Mass.) Deed Reform. In order to improve research at the Suffolk Registry of Deeds, Hassam helped get the twelve volumes of Suffolk County deeds printed. He wrote the introduction to each volume and supervised the creation of indices. Subseries C. Genealogical Research consists of correspondence regarding the work he did on family histories. Subseries D. Military Records contains records relating to his military service in the 75th United States Colored Infantry during the American Civil War, his diary while serving, and his veteran activities after the war. Subseries E. Financial Records consists of household receipts for clothing, food, books, furniture and the like.

Series II. Nelly Alden Batchelder Hassam Papers has been arranged into three subseries: Correspondence and Memorabilia, Financial Records, and Diaries and Other Writings. Subseries A. Correspondence and Memorabilia includes correspondence, memorabilia, photographs, calling cards, newspaper clippings, and more. Of special note is an autograph book (1856-1870), given to Nelly by her mother in 1879, which records the signatures of President Franklin Pierce and members of his Cabinet and Congress. It was a gift from Joseph Smith, Jane Reed Smith Batchelder's cousin in 1856. Subseries B. Financial Records consists of an account book and receipts. Subseries C. Diaries and Other Writings includes diaries, an inventory of houses in Boston and Salem, a scrapbook, and genealogy of the Batchelder family and other families, including biographical sketches of family members John H. Batchelder, Jane Reed (Smith) Batchelder, Eleanor Hassam, and Nelly herself.

Series III. Eleanor Hassam Papers includes correspondence, diaries, a scrapbook made by her mother about family members, and school work.

Series IV. John Henry Batchelder Papers includes correspondence, financial records, papers and a register from his dental practice, papers from his time in government service, and congratulations on his 50th wedding anniversary.

Series V. Hassam Family Members' Papers is divided into two subseries: A. Jonathan Hassam and B. Other Family Members. It contains mostly correspondence to and from various family members. Subseries A. Jonathan Hassam (John Tyler Hassam's grandfather) contains correspondence, an account book, and some documentation pertaining to the time he was in Naples, Italy in the summer of 1809; he was in command of the Johanna (Ship) and captured by the English Man-of-War Espoir. They were carried into Malta where a prize court declared the capture illegal and ordered the restoration of the vessel and cargo. Subseries B. Other Family Members includes papers from John Hassam, John Tyler Hassam's father; Frederick W. Hassam, John Tyler's, brother; Jane Reed Smith, Nelly's mother; and Josiah Smith, Nelly's grandfather, who was a member of the United States Congress. The letter from Josiah Smith mentions a Congressional session discussing Negros escaping from their masters. Also included are a copy of a letter from Josiah Smith to his children and a letter from Mary B. Cushing to her sister, Sarah.