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 northwest of Pittsburgh near the Pennsylvania–Ohio border, approximately 17 miles 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.