High Quality Content by WIKIPEDIA articles! Bergen County is the most populous county of the state of New Jersey, United States. As of the 2010 United States Census, its population was 905,116. The county is part of the New York City Metropolitan Area. Its county seat is Hackensack. Bergen County ranked 16th among the highest-income counties in the United States in 2009 in terms of per-capita income, while simultaneously hosting a park system totaling nearly 9,000 acres.