PLAINFIELD, a city of Union county, New Jersey, U.S.A., about 24 m. W. by S. of New York City. Pop. (1910 U.S. census), 20,550. It is served by the Central Railroad of New Jersey and by electric lines connecting with neighbouring towns. It is situated for the most part on a plain; north-east are heights occupied by the suburb of Netherwood, and north in Somerset county, on the slope of the first Watchung Mountain, is the borough of North Plainfield (pop. 1910 U.S. census, 6117), which forms with Plainfield virtually a single residential and business community. Plainfield is one of the most attractive residential suburbs of New York. The city has an excellent public school system, a good public library, with an art gallery and museum. The Muhlenberg hospital, club houses and a driving track are features of the city. The value of the factory products increased from $2,457,454 in 1900 to $5,572,154 in 1905, or 46·6%. Plainfield was settled in 1684, but it was not until 1755 that the first frame house was erected. In 1760 a grist mill was erected, and for several years the place was called Milltown. The township of Plainfield was created out of Westfield township in 1847, and in 1867 Plainfield was chartered as a city.