South Hackensack is a township in Bergen County, New Jersey, United States. As of the 2010 United States Census, the township's population was 2,378, reflecting an increase of 129 from the 2,249 c…South Hackensack is a township in Bergen County, New Jersey, United States. As of the 2010 United States Census, the township's population was 2,378, reflecting an increase of 129 from the 2,249 counted in the 2000 Census, which had in turn increased by 143 from the 2,106 counted in the 1990 Census.