Armonk is a hamlet and census-designated place (CDP) located in the town of North Castle in Westchester County, New York. As of the 2000 census, the CDP population was 3,461. Armonk is home to the global headquarters of information technology company IBM and bond insurer MBIA, and the Americas headquarters of reinsurer Swiss Re. Smith's Tavern, an historical site and landmark of the Revolutionary War, is located in Armonk and is the home of the North Castle Historical Society. The North Castle Public Library, a member of the Westchester Library System, is also located in Armonk.