The Rufus King collection documents the career of Federalist Rufus King as a New York Assemblyman, U.S. Senator, US Minister to Great Britain, Federalist party leader, and candidate for Presidency and Vice-Presidency. Although the bulk of the collection is official and private correspondence, it also consists of notes, memoranda, diaries, essays, account books, newspaper articles, and a few legal documents. The collection also has the notes and letters dated from 1894-1899 of Charles R. King, Rufus King's grandson, who edited his grandfather's papers for the six volume The Life and Correspondence of Rufus King. Many of Rufus King's notebooks include later memoranda from Charles R. King commenting on the text.

The collection principally covers eighteenth and early nineteenth century politics in early America and England. Specific topics documented include the Constitutional Convention of 1787, King's opposition to the War of 1812, the Navigation Act of 1818, the Missouri Compromise, and the administration and sale of public lands. It also describes negotiations between the United States and Great Britain over the Jay Treaty, Barbary affairs, South American independence, the East India Trade, the Fugitive Slave Acts, and the British-French negotiations in 1803.

A large amount of material is correspondence with American political figures such as John Adams, John Quincy Adams, Alexander Hamilton, William Hindman, Charles Jared Ingersoll, John Jay, John Alsop King, Charles King, Nicholas Low, James Madison, Gouverneur Morris, Timothy Pickering, Thomas Pinkney, Granville Sharp, John Trumbull, George Washington, and Noah Webster. Others represented in the correspondence include Francisco de Miranda, Joseph Pitcairn, John Alsop, Juan Pablo Viscardo y Guzman, George Canning, and Henry Clay. The collection also contains documents and correspondence of family members Richard King, John A. King, and Charles King.

The personal material of Rufus King includes his correspondence, household account books, a 1802 diary kept while traveling in Europe, and an inventory of his library. It also consists of notebooks, diaries, and essays containing King's observations on his contemporaries and domestic and foreign politics. Some of his notebooks include extracts from books read by King along with his own comments and observations.

This collection supports research on the nuances of King's lengthy political career as well as the early political history of the United States.