North Plainfield is a borough in Somerset County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 21,936, reflecting an increase of 833 (+3.9%) from the 21,103 counted in the 2000 Census, which had in turn increased by 2,283 (+12.1%) from the 18,820 counted in the 1990 Census.
North Plainfield Township was created from portions of Warren Township by an act of the New Jersey Legislature passed on April 2, 1872. The borough of North Plainfield became an independent municipality on June 9, 1885. The name derives from Plainfield, which derived its name from a local estate or from its scenic location.
In 1902, the New Jersey Legislature approved measures that would have allowed the borough to become part of Union County (a measure repealed in 1903) and to allow for a merger of North Plainfield with the City of Plainfield subject to the approval of a referendum by voters in both municipalities.
North Plainfield is home to the Washington Park Historic District.
According to the United States Census Bureau, North Plainfield borough had a total area of 2.82 square miles (7.31 km2), including 2.81 square miles (7.27 km2) of land and 0.01 square miles (0.03 km2) of water (0.46%).
The borough is bordered by the municipalities of Watchung to the north, Green Brook Township to the southwest, all in Somerset County; and to the south by Plainfield in Union County.
North Plainfield is in the northern division of the Raritan Valley along with Green Brook.
The 2010 United States Census counted 21,936 people, 7,448 households, and 5,266 families in the borough. The population density was 7,850.0 inhabitants per square mile (3,030.9/km2). There were 7,848 housing units at an average density of 2,808.5 per square mile (1,084.4/km2). The racial makeup was 55.01% (12,066) White, 18.85% (4,134) Black or African American, 0.29% (63) Native American, 5.81% (1,275) Asian, 0.05% (12) Pacific Islander, 16.00% (3,510) from other races, and 3.99% (876) from two or more races. Hispanic or Latino of any race were 44.21% (9,699) of the population.
Of the 7,448 households, 35.8% had children under the age of 18; 48.3% were married couples living together; 15.0% had a female householder with no husband present and 29.3% were non-families.