Richland, city (1990 pop. 32,315), Benton co., S Wash., at the confluence of the Columbia and Yakima rivers, in an irrigated farm and vineyard region; inc. 1958. It is the headquarters of the U.S. Department of Energy's Hanford Nuclear Reservation (620 sq mi/1,606 sq km), on which the city's economy is based. With Kennewick and Pasco it forms a tricity area that grew during World War II. The area was settled in 1910, and a small farming hamlet there was taken over (1942) by the U.S. government for a plutonium plant to be used in the production of nuclear weapons for the Manhattan Project; the B Reactor there is now a national historic landmark. The city of Richland was built (1943–45) to house employees of the project. Federal ownership and management of the city were gradually relinquished after World War II, with complete self-governance coming in 1958. Plutonium production at Hanford continued into the 1980s. Since the 1990s the Department of Energy's work there has been focused on waste management and environmental cleanup, while the city has sought to diversify its economy.