New Castle is a city in and the county seat of Lawrence County, Pennsylvania, United States. Located along the Shenango River at the mouth of Neshannock Creek, it is 43 miles (69 km) northwest of Pittsburgh near the Pennsylvania–Ohio border, approximately 17 miles (27 km) southeast of Youngstown, Ohio. As of the 2020 census, the city had a population of 21,926. The commercial center of a fertile agricultural region, New Castle is included in the northwestern part of the Pittsburgh metropolitan area.

Lawrence County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 86,070. The county seat and largest city is New Castle.