Butler is a borough in Morris County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 7,539, reflecting an increase of 119 from the 7,420 counted in the 2000 Census, which had in turn increased by 28 from the 7,392 counted in the 1990 Census.Butler was incorporated as a borough by an act of the New Jersey Legislature on March 13, 1901, from portions of Pequannock Township.