Mercer County is a county located in the U.S. state of New Jersey. Its county seat is Trenton, the state capital. It is officially part of both the New York metropolitan area and Delaware Valley, due to it being close to New York City and Philadelphia, as well as the Trenton-Ewing Metropolitan Statistical Area. As of 2007, the Trenton-Ewing MSA is ranked 136th in the list of U.S. Metropolitan Statistical Areas for total population at 365,449.
The county is named for Continental Army General Hugh Mercer, who died at the Battle of Princeton in 1777. The Mercer Oak, against which the dying general rested as his men continued to fight, appears on the county seal. As of the United States 2000 Census, the population was 350,761, estimated to have risen to 367,605 as of 2006. Mercer County ranks 79th among the highest-income counties in the United States. It also is ranked 57th in the United States by per capita income.
Mercer county is home to Princeton University, Princeton Theological Seminary, Institute for Advanced Study, Rider University, The College of New Jersey, Thomas Edison State College and Mercer County Community College.