New Castle is a city in Lawrence County, Pennsylvania, 50 miles northwest of Pittsburgh, Pennsylvania; in 1910, the total population was 36,280; in 1920, 44,938; and in 1940, 47,638. The population was 26,309 at the 2000 census. It is the county seat of Lawrence County. It is the commercial centre of a fertile agricultural region. New Castle is a prime example of a Rust Belt city which has been forced to adapt to changing economic situations. New Castle apartments for rent comparison page shows most up to date rent information on New Castle apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.