Millburn is a suburban township in Essex County, New Jersey, United States. As of the 2010 United States Census, the township's population is 20,149, reflecting an increase of 384 (+1.9%) from the 19,765 counted in the 2000 Census, which had in turn increased by 1,135 (+6.1%) from the 18,630 counted in the 1990 Census. Short Hills is an upscale section and unincorporated community within Millburn. The township is home to the South Mountain Reservation, The Mall at Short Hills and the Paper Mill Playhouse, an established regional theater.