Sosnowiec (sôsnôˈvyĕts) [key], Ger. Sosnowitz, city (1993 est. pop. 258,500), Śląskie prov., S Poland. A center of the Katowice mining and industrial region, it has coal mines, ironworks, and steelworks and various other heavy industrial plants. Sosnowiec passed to Prussia in 1795, to Russia in 1815, and reverted to Poland in 1919. The city has a 17th-century castle.