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 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.