Horatio King (June 21, 1811 - May 20, 1897) was Postmaster General of the United States under James Buchanan.

Born in Paris, Maine, he received a common school education, and at the age of 18 entered the office of the Paris Jeffersonian, where he learned printing, afterward becoming owner and editor of the paper. In 1833 he moved it to Portland, where he published it until 1838. In 1839 he went to Washington, D.C., having been appointed clerk in the post office department, and was gradually promoted. In 1854 he was appointed first Assistant Postmaster General, and in January, 1861, while acting as Postmaster General, he was questioned by a member of Congress from South Carolina with regard to the franking privilege. In his reply, King was the first officially to deny the power of a state to separate from the Union. He was then appointed Postmaster General, serving from February 12 until March 7, 1861.

On retiring from office he remained in Washington, D.C. during the Civil War, serving on a board of commissioners to carry into execution the emancipation law in the District of Columbia. His efforts led to a considerable number of former slaves settling in the District.

After his retirement from office, King practiced in Washington as an attorney before the executive department and international commissions. He was active in procuring the passage of three acts in 1874, 1879, and 1885 respectively, requiring the use of the official "penalty envelope," which has secured a large saving to the government. He also took an active part in the work of completing the Washington Monument, serving as secretary of the Monument Society from 1881. King was a frequent contributor to the press, and published An Oration before the Union Literary Society of Washington (Washington, D.C., 1841), and Sketches of Travel; or, Twelve Months in Europe (1878). His son Horatio Collins King was also a notable figure.

Prior to his death, King had been the last surviving member of the Buchanan Cabinet. Further information about this individual or organization may be available in the Special Collections Research Center Wiki: .