Middlesex County is a county located in north-central New Jersey, United States. As of 2015, Middlesex County's Census-estimated population was 840,900, an increase of 3.8% from the 2010 United States Census, when its population was enumerated at 809,858, making it the second-most populous county in the state. Middlesex is part of the New York metropolitan area, and its county seat is New Brunswick. The center of population of the state of New Jersey is located in Middlesex County, in East Brunswick Township, just east of the New Jersey Turnpike. The 2000 Census showed that the county ranked 63rd in the United States among the highest-income counties by median household. The Bureau of Economic Analysis ranked the county as having the 143rd-highest per capita income of all 3,113 counties in