NEW CASTLE, a post-borough of the United States, the capital of Lawrence county, Pennsylvania, 2 miles above the junction of the Shenango and Mahoning (subtributaries of the Ohio), and 45 miles north-north-west of Pittsburg. It contains blast furnaces, rolling-mills, iron and brass foundries, tube-works, boiler-works, machine shops, planing-mills, nail factories, glass-works, grist-mills, and breweries. The population increased from 6164 in 1870 to 8418 in 1880, and was estimated at upwards of 13,000 in 1883.