Papers of William Sidney Mount include correspondence, diaries, scrapbooks, notebooks, invitations, exhibit catalogs, business papers and miscellaneous printed materials.

Letters, deeds, title abstracts, legal notices, maps, bills and other papers concerning land sales and transactions, as well as book catalogs, scrapbooks, postcards and other material. Papers relate to the Deer Range Estate and Lakeland property in the town of Islip, the Point O’ Woods Association, the Long Island Chautauqua Assembly Association, and other properties on Long Island. There are maps of various villages and developments including Lakeland, Saltaire, Bohemia, Setauket and Stony Brook. Also, petitions, complaints, summonses, judgements, testimony and other documents from a lawsuit brought by Ackerly against the Southside Sportsman Club.

Julia Ann Hawkins (1782-1841) was the daughter of Jonas Hawkins of Stony Brook. Her brothers included Micah Hawkins and Jonas Hawkins, Jr. She married Thomas Shepard Mount (1778-1814) of Setauket. Among their children were the artists Henry Smith Mount, Shepard Alonzo Mount and William Sidney Mount. Papers of Hawkins family members include military papers of Jonas Hawkins, (both Sr. and Jr.), bonds, receipts and other papers of Jonas Hawkins, Jr., as postmaster at Setauket, c1815; correspondence, receipts, librettos of Micah Hawkins, including a libretto of his opera The Saw Mill, and probate of his will, 1833. Papers of the children of Julia Hawkins and Thomas Shepard Mount and their descendants include family correspondence, copy books, poems, songs, diaries, accounts, guardianship papers, wills, deeds, legal papers, postcards, photographs and other material of Henry Smith Mount, Robert Nelson Mount, Shepard Alonzo Mount, Elizabeth Elliot Mount, Robert Henry Mount, Evelina Mount, Ruth Mount Seabury, and others. Items of note include papers of Judge Thomas Shepard Mount (1834-1900) concerning the Stony Brook school district, 1870-1899; correspondence of John Brewster Mount with Orville B. Ackerly, 1901; correspondence, clippings, genealogical material and historical notes of various museums concerning Mount art work and family history. Papers of Malcolm Mount (son of Henry Smith Mount) who moved to Gilroy, California, and his daughter Sarah Fisher (“Daisy”) Mount, include letters, photographs, postcards, diaries, certificates and contracts of Sarah F. Mount with the San Francisco School Board, and letters to Sarah from a Japanese-American friend who was sent to an internment camp in Utah, 1942-1945. Also, deeds, wills, title abstracts, maps and other documents relating to family property in Stony Brook and Smithtown; an agreement between Charles Q. Archdeacon and Edward P. Buffet about the sale of the Hawkins-Mount house, and correspondence between Edward P. Buffet and Orville B. Ackerly.

Diaries of the Rev. Alexander Huntington Clapp of Providence, Rhode Island and Boston, and of his wife, Emily Copland Clapp; also an inventory of Rev. Clapp’s library, a record of sermons preached, and miscellany.