The New Castle Court House Museum is the center of a circle with a 12-mile radius that defines most of the border between the states of Delaware and Pennsylvania and parts of the borders between Delaware and New Jersey and Maryland.

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.