High Quality Content by WIKIPEDIA articles! Union Township is a Township in Hunterdon County, New Jersey, United States. As of the United States 2010 Census, the township population was 5,908. The southwest half of the township lies on what is known as the Hunterdon Plateau, the northwest corner consists of the Musconetcong Ridge and the northeast section is part of the lower-lying Newark Basin around Spruce Run Reservoir.