Butler is a borough in Morris County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 8,047, an increase of 508 from the 2010 census count of 7,539, which in turn reflected an increase of 119 from the 7,420 counted in the 2000 census. Butler was incorporated as a borough by an act of the New Jersey Legislature on March 13, 1901, from portions of Pequannock Township.