Pierre (pēr) [key], city (1990 pop. 12,906), state capital (since 1889) and seat of Hughes co., central S.Dak., on the east bank of the Missouri River, opposite Fort Pierre; inc. 1883. Its economy is centered around agriculture (chiefly grains and cattle), tourism, and the state government. Electrical and irrigation equipment are manufactured. Originally the fortified capital of the Aricara, Pierre served as the trade center of the middle Missouri River from 1822 to 1855. From 1876 to 1885 it was the steamboat head for the Black Hills gold trade. The city boomed with the arrival of the railroad (1880), becoming an important trading and shipping center for a farm and ranch area. The Pierre Indian Learning Center is there, as is the South Dakota Discovery Center and Aquarium. Oahe Dam, a major unit of the Missouri River basin project, is nearby.