Letters to Flagg from political figures of the Jackson-Van Buren era. The correspondence is particularly useful in shedding light on the conduct of the national campaign of 1848, when Van Buren ran as an independent candidate for the presidency. There are 90 letters written to Flagg, among which are 41 from Martin Van Buren, 34 from Preston King, and nine from John A. Dix.

Papers of the Jay family and of those families related to the Jay family, including Bruen, Butterworth, Chapman, Clarkson, Dawson, Du Bois, Field, Iselin, McVickar, Mortimer, O'Kill, Pellew, Pierrepont, Prime, Robinson, Schieffelin, Von Schweinitz, Sedgwick, and Wurts. In addition to family and personal matters, the correspondence deals with anti-slavery, New York State civil service, repeal of the Missouri Compromise, the Civil War, the Blair Bill, international affairs, and New York City and State politics and government. There are letters from numerous prominent persons including George Bancroft, F.A.P. Barnard, Bismarck, William Cullen Bryant, Aaron Burr, James Fenimore Cooper, Ralph Waldo Emerson, Hamilton Fish, Albert Gallatin, Horace Greeley, Nathaniel Hawthorne, Oliver Wendell Holmes, Washington Irving, Frances Anne Kemble, Jenny Lind, Henry W. Longfellow, Seth Low, James Russell Lowell, John Stuart Mill, Alice Duer Miller, Clement Clarke Moore, J.P. Morgan, Thomas Nast, Commodore Matthew Perry, Franklin D. Roosevelt, Theodore Roosevelt, Elihu Root, Carl Schurz, William H. Seward, William T. Sherman, Charles Sumner, and John Greenleaf Whittier.

Papers dealing with Johnson's public life in New York City and in the New York State Senate. While Assistant Alderman, Johnson received numerous letters of application from citizens seeking patronage for a variety of municipal offices, ranging from requests to be a night watchman to a position as a municipal court justice. Also, letters, reports, and other documents relating to various municipal services such as health, welfare, fire fighting, street maintenance, water, sewers, railroads, ferries, and stage coaches. Some letters and documents concern Whig Party politics in the 3rd Ward. Johnson's correspondence as a New York Society Library Trustee refers to the proposed merger with the New York Athenaeum. Also, twelve items relating to his term in the State Senate, covering taxation and control of foreign laborers.