New Castle is a city in New Castle County, Delaware, United States. The city is located six miles (10 km) south of Wilmington and is situated on the Delaware River. As of 2020, the city's population was 5,551. New Castle constitutes part of the Delaware Valley or Philadelphia metropolitan area.

Wilmington is the largest city in the U.S. state of Delaware. The city was built on the site of Fort Christina, the first Swedish settlement in North America. It lies at the confluence of the Christina River and Brandywine Creek, near where the Christina flows into the Delaware River. It is the county seat of New Castle County and one of the major cities in the Delaware Valley metropolitan area. Wilmington was named by Proprietor Thomas Penn after his friend Spencer Compton, Earl of Wilmington, who was prime minister during the reign of George II of Great Britain.