The Township of Mahwah is the northernmost and largest municipality by geographic area (26.19 square miles (67.8 km2)) in Bergen County, New Jersey, United States. As of the 2010 United States Census, the population of the township was 25,890, an increase of 1,828 (+7.6%) from the 24,062 counted in the 2000 Census, which had in turn increased by 6,157 (+34.4%) from the 17,905 counted in the 1990 Census.