Walpack Township is a township in Sussex County, in the U.S. state of New Jersey. As of the 2020 United States census, the township's population was 7, a decrease of 9 from the 2010 census count of 16, which in turn reflected a decline of 34 from the 41 counted in the 2000 census. Walpack Township was the smallest municipality by populati…Walpack Township is a township in Sussex County, in the U.S. state of New Jersey. As of the 2020 United States census, the township's population was 7, a decrease of 9 from the 2010 census count of 16, which in turn reflected a decline of 34 from the 41 counted in the 2000 census. Walpack Township was the smallest municipality by population and one of only four municipalities in New Jersey with a population under 100 as of the 2020 Census; it had the state's third-smallest population in the 2010 census, behind Tavistock and the now-defunct Pine Valley, both in Camden County.