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.
It is one of the oldest courthouses in the United States and has played a role in a number of historic events. It was declared a National Historic Landmark in 1972. The building is also a contributing property to a second National Historic Landmark, the New Castle Historic District. It is part of First State National Historical Park.
Wikipedia https://en.wikipedia.org/wiki/New_Castle_Court_House_Museum
Coordinates 39°39'35.378" N -75°33'48.971" E