New Castle is a city in
Lawrence County,
Pennsylvania,
United States, northwest of
Pittsburgh and near the Pennsylvania-Ohio border just east of
Youngstown, Ohio; in 1910, the total population was 36,280; in 1920, 44,938; and in 1940, 47,638. The population has fallen to 23,128 according to the
2010 census. It is the
county seat of
Lawrence County. New Castle is the principal city of the
New Castle, PA Micropolitan Statistical Area and a part of the
Pittsburgh-New Castle-Weirton, PA-OH-WV Combined Statistical Area, which is the 20th largest in the
United States. It is the commercial center of a fertile agricultural region.