Fanwood is a borough in Union County, in the U.S. state of New Jersey. Located on a ridge in northern-central New Jersey, the borough is a commuter town of New York City in the New York metropolitan area. Fanwood is located in the Raritan Valley and Rahway Valley regions. As of the 2020 United States census, the borough's population was 7,774, an increase of 456 from the 2010 census count of 7,318, which in turn reflected an increase of 144 from the 7,174 counted in the 2000 census.