Millburn is a suburban township in southwestern Essex County, within the U.S. state of New Jersey, and part of the New York metropolitan area. As of the 2020 United States census, the township's population was 21,710, its highest decennial count ever and an increase of 1,561 from the 20,149 recorded at the 2010 census, which in turn reflected an increase of 3…Millburn is a suburban township in southwestern Essex County, within the U.S. state of New Jersey, and part of the New York metropolitan area. As of the 2020 United States census, the township's population was 21,710, its highest decennial count ever and an increase of 1,561 from the 20,149 recorded at the 2010 census, which in turn reflected an increase of 384 from the 19,765 counted in the 2000 census. Short Hills, with a 2020 population of 14,422, is an unincorporated community and census-designated place located within Millburn that is home to most of the township's population.