Västerås (vĕsˌtərōsˈ) [key], city (1990 pop. 98,303), capital of Västmanland co., E Sweden, a port on Lake Mälaren at the mouth of the Svartån River. It is the main center of the Swedish electrical goods industry; other manufactures include metal goods, textiles, and glass. Founded by 1100, Västerås was one of Sweden's great medieval cities, with a cathedral (13th cent.) and a fortified castle (14th cent.). Eleven important diets convened there, notably the Västerås Recess (1527), which created the Lutheran state church, and the diet of 1544, which made the Swedish throne hereditary.