Hackensack is a city in Bergen County, New Jersey, United States, and serves as its county seat. It was officially named New Barbadoes Township until 1921, but it was informally known as Hackensack. As of the 2010 United States Census, the city's population was 43,010, reflecting an increase of 333 (+0.8%) from the 42,677 counted in the 2000 Census, which had, in turn, increased by 5,628 (+15.2%) from the 37,049 counted in the 1990 Census.