South Plainfield is a borough in northern Middlesex County, in the U.S. state of New Jersey. The borough is situated on the border with Union County in the Raritan Valley region, within the New York metropolitan area. As of the 2020 United States census, the borough's population was 24,338, its highest decennial count ever and an increase of 953 (+4.1%) from the 23,385 recorded at the 2010 census, which in turn reflected an increase of 1,575 (+7.2%) from the 21,810 counted in the 2000 census.

The New Jersey Senate is the upper house of the New Jersey Legislature by the Constitution of 1844, replacing the Legislative Council. There are 40 legislative districts, representing districts with an average population of 232,225. Each district has one senator and two members of the New Jersey General Assembly, the lower house of the legislature. Prior to the election in which they are chosen, senators must be a minimum of 30 years old and a resident of the state for four years to be eligible to serve in office.