The collection consists primarily of correspondence, documents, and miscellaneous material of William Worth Belknap (Princeton Class of 1848) and his father, William Goldsmith Belknap (1794-1851), of Newburgh, New York. Included are official correspondence of William Goldsmith Belknap, a career soldier, covering his service in the army at the battle of Fort Erie, Canada, during the War of 1812, in Florida (1841-1843) during the Seminole War, and in Texas (1844-1851), where he fought in the Mexican-American War. Correspondents include William Jenkin Worth, J. T. Sprague, and Henry Whitney. There is also a series of letters (1835-1851), to his wife, Anne Clark Belknap, from various military posts in the Southwest, Florida, and Texas.

William Worth Belknap settled in Keokuk, Iowa, in 1851. The papers include his official correspondence and documents relating to his service with the 15th Iowa Infantry in the Civil War and, afterwards, as collector of internal revenue in Iowa (1865-1869), but they mainly concern his trial and impeachment on charges of receiving bribes for appointments of post-traders at Fort Sill, Indian Territory (Oklahoma), while serving as secretary of war (1869-1876). There are letters by Chester Alan Arthur, Ulysses S. Grant, and Philip Sheridan, as well as a large file of family correspondence, including correspondence of Belknap's sister, Clara Belknap Wolcott, and other Wolcott family members. Also present are Civil War ordnance and casualty records, tax reports, War Department reports, a few photographs, printed matter, and genealogical material.