Mercer County is a county located in the U.S. state of New Jersey. Its county seat is Trenton, the state capital. The county is part of the Trenton, NJ Metropolitan Statistical Area and is considered part of the New York metropolitan area by the United States Census Bureau, but also directly borders the Philadelphia metropolitan area and is included within the Federal Communications Commission's Philadelphia Designated Market Area. As of 2014, Mercer County's Census-estimated population was 371,537, an increase of 1.4 rom the 2010 United States Census, when its population was enumerated at 366,513, in turn an increase of 15,752 (4.5%) from the 350,761 enumerated in the 2000 Census, retaining its position as the 12th-most populous county in the state. Mercer County stands among the highest-income counties in the United States, with the Bureau of Economic Analysis having ranked the county as having the 78th-highest per capita income of all 3,113 counties in the United States (and the sixth-highest in New Jersey) as of 2009.