Trenton is the capital city of the U.S. state of New Jersey and the county seat of Mercer County. It briefly served as the capital of the United States in 1784. The city's metropolitan area, consisting of Mercer County, is grouped with the New York Combined Statistical Area by the United States Census Bureau, but it directly borders the Philadelphia metropolitan area and was from 1990 until 2000 part of the Philadelphia Combined Statistical Area.