Correspondence, manuscripts, documents, notes, photographs, transcripts of historical documents, and printed materials. Larson's correspondence consists of professional correspondence relating to historical research; his work at the United States National Archives, including correspondence with Philip Hamer while preparing a special survey of archival materials in the U.S. Virgin Islands under a Works Progress Administration grant, 1936-1937; genealogical research; and personal correspondence with family and friends. Manuscripts by Larson relate to Alexander Hamilton, Bjørnson, Bjørnstjerne, Danish National Archives, archival research in the U. S. Virgin Islands, and the U.S. Army activities in Korea and in the Virgin Islands.

Manuscripts by other authors are historical articles on the Virgin Islands. Larson's research notes are index cards and loose leaf notes on Alexander Hamilton, the history of the Virgin Islands, graduate and undergraduate student course notes, and notes for classes which Larson taught. Historical documents include surveys and statistical information on the U.S. National Archives project in the Virgin Islands, typescripts of 19th and 20th century newspaper articles and government reports published in the Virgin Islands, and handwritten or typescript copies of 18th century documents relating to Alexander Hamilton. Personal Documents contain copies of Larson's applications for federal employment, certificates, diplomas, student report cards, and obituaries. Photographs are of the Larson family and of Nelson Rockefeller. Printed Materials consists of books inscribed to Larson.