Newark is a city in New Castle County, Delaware, United States. It is located 12 miles west-southwest of Wilmington. According to the 201…Newark is a city in New Castle County, Delaware, United States. It is located 12 miles west-southwest of Wilmington. According to the 2010 census, the population of the city is 31,454. The University of Delaware is located here. The city constitutes part of the Delaware Valley, and the Philadelphia metropolitan area.