Correspondence, diaries, speeches, writings, biographical notes, scrapbooks, newspaper clippings, printed matter, and other papers relating chiefly to Hamlin's service in the U.S. Dept. of the Treasury and the Federal Reserve System; Hamlin's civic affairs; and his family's social life in Washington, D.C. Topics include leaders and policies of the Democratic Party especially during the Grover Cleveland, Woodrow Wilson, and Franklin D. Roosevelt administrations and Hamlin's law practice in Boston, Mass. Includes copies of Huybertie Pruyn Hamlin's manuscript pertaining to the Hamlin, Pruyn, and Roosevelt families and to social visits (November 1941-January 1942) to the White House where guests included Winston Churchill and other prominent leaders; diaries and scrapbooks of the Hamlin's daughter, Anna Hamlin; and genealogical information concerning the Hamlin family. Of special interest is an original cartoon depicting Hamlin drawn by Sebastian T. Robles for the Washington Post.

Correspondents include Newton Diehl Baker, John H. Clarke, Frances Folsom Cleveland, Grover Cleveland, Josephus Daniels, Edith Benham Helm, Herbert Hoover, Cordell Hull, Robert Lansing, Henry Cabot Lodge, William Gibbs McAdoo, William McKinley, Levi P. Morton, Richard Olney, George Foster Peabody, Franklin D. Roosevelt, Theodore Roosevelt, William H. Taft, and Woodrow Wilson.