Warren County is a county located in the U.S. state of New Jersey. As of the 2010 United States Census, the population was 108,692. Its county seat is Belvidere. It is part of the Allentown-Bethlehem-Easton, PA-NJ metropolitan area and is generally considered the eastern border of the Lehigh Valley.
Warren County was incorporated by an Act of the New Jersey Legislature on November 20, 1824, from portions of Sussex County. At its creation, the county consisted of the townships of Greenwich, Independence, Knowlton, Mansfield, Oxford, and Pahaquarry (now defunct).