High Quality Content by WIKIPEDIA articles! Washington Township is a Township in Warren County, New Jersey, United States. As of the United States 2010 Census, the township population was 6,651. It is part of the eastern most region of the Lehigh Valley. It is one of six municipalities in New Jersey under the name Washington (one of which is a borough, five of which are townships). In fact, Washington Township, Warren county completely surrounds the borough of Washington. Mansfield Township, also in Warren County, borders both this municipality and an unrelated township in Morris County also known as Washington Township.