South New Castle is a borough in central Lawrence County, Pennsylvania, United States.

[4] It is primarily a residential community which lies south of the city of New Castle, and is part of the Pittsburgh metropolitan area.

[5] According to the United States Census Bureau, the borough has a total area of 0.3 square mile (0.9 km2), all land.

The racial makeup of the borough was 99.38% White, 0.37% Native American, 0.12% Asian, and 0.12% from two or more races.

Its chili dogs are the product of Greek immigrants who came to New Castle in the early 1900's and established restaurants along with their homes.