Montclair (/mɒn(t)ˈklɛər/) is a township in Essex County in the U.S. state of New Jersey. Situated on the cliffs of the Watchung Mountains, Montclair is a wealthy and diverse commuter town and suburb of …Montclair (/mɒn(t)ˈklɛər/) is a township in Essex County in the U.S. state of New Jersey. Situated on the cliffs of the Watchung Mountains, Montclair is a wealthy and diverse commuter town and suburb of New York City within the New York metropolitan area. As of the 2020 U.S. census, the township's population was 40,921, reflecting an increase of 3,234 from the 37,687 counted in the 2010 Census. As of 2010, it was the 60th-most-populous municipality in New Jersey.