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. As of the 2010 United States Census, Trenton had a population of 84,913, making it the state's 10th-largest municipality after having been the state's ninth-largest municipality in 2000. The population declined by 490 from the 85,403 counted in the 2000 Census, which had in turn declined by 3,272 from the 88,675 counted in the 1990 Census. The Census Bureau's Population Estimates Program calculated that the city's population was 83,203 in 2019, ranking the city the 413th-most-populous in the country.
Trenton dates back at least to June 3, 1719, when mention was made of a constable being appointed for Trenton while the area was still part of Hunterdon County. Boundaries were recorded for Trenton Township as of March 2, 1720.