Flemington is a borough in Hunterdon County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 4,581, reflecting an increase of 381 (+9.1%) from the 4,200 counted in the 2000 Census, which had in turn increased by 153 (+3.8%) from the 4,047 counted in the 1990 Census. It is the county seat of Hunterdon County. Most of the borough is in the Amwell Valley (a low-lying area of the Newark Basin), but northwest portions of the borough sit on the Hunterdon Plateau.