Passaic (/pəˈseɪ.ᵻk/pə-SAY-ik or local /pəˈseɪk/pə-SAYK) is a city in Passaic County, New Jersey, United States. As of the 2010 United States Census, the city had a total population of 69,781, maintaining its status as the 15th largest municipality in New Jersey with an increase of 1,920 residents (+2.8%) from the 2000 Census population of 67,861, which had in turn increased by 9,820 (+16.9%) from the 58,041 counted in the 1990 Census. Passaic is the tenth most densely populated municipality in the entire United States with 22,000+ people per square mile.
Located north of Newark on the Passaic River, it was first settled in 1678 by Dutch traders, as Acquackanonk Township. The city and river draw their name from the Lenape word "pahsayèk" which has been variously attributed to mean "valley" or "place where the land splits."