Trenton is the capital city of the U.S. state of New Jersey and the seat of Mercer County. It was the capital of the United States from November 1 until December 24, 1784. Trenton and Princeton are the two principal cities of the Trenton–Princeton metropolitan statistical area, which encompasses those cities and all of Mercer County for statistical purposes and constitutes part of the New York combined statistical area by the U.S. Census Bureau.