New Castle is a city in Lawrence County, Pennsylvania, United States, and its county seat. 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. The city had a population of 21,926 as of the 2020 census. The commercial center of a fertile agricultural region, New Castle is included in the northwestern fringes of the Pittsburgh metropolitan area.