New Castle
- County:
- Lawrence County
- County Seat:
- Yes
- Area (mi²):
- 8.307
- State:
- Pennsylvania
New Castle is a city located in Lawrence County, Pennsylvania. New Castle has a 2026 population of 21,332. It is also the county seat of Lawrence County. New Castle is currently declining at a rate of -0.48% annually and its population has decreased by -2.59% since the most recent census, which recorded a population of 21,900 in 2020.