Passaic 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 from the 2000 Census population of 67,861, which had in turn increased by 9,820 from the 58,041 counted in the 1990 Census. The Census Bureau's Population Estimates Program calculated that the city's population was 69,703 in 2019, ranking the city the 524th-most-populous in the country. Among cities with more than 50,000 people, Passaic is the fifth-most-densely-populated municipality in the United States, with more than 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."