New Jersey had gained a fourteenth seat following the 1930 census, and reached its historic maximum of fifteen in 1963. After the elimination of the 15th, New Jersey was left with 14 seats in the House of Representatives until 1993, when it was reduced to 13 as a result of the 1990 census.
In 1970, the district's borders largely overlapped those of Middlesex County, and a large majority of the county was in the 15th district.