South Dakota spending, because of the proximity of many tourist attractions in the Black Hills and Ellsworth Air Force Base. The next eight largest cities in the state, in order of descending 2010 population, are Aberdeen (26,091), Brookings (22,056), Watertown (21,482), Mitchell (15,254), Yankton (14,454), Pierre (13,646), Huron (12,592), and Vermillion (10,571). Pierre is the state capital, and Brookings and Vermillion are the locations of the state's two largest universities (South Dakota State University and University of South Dakota, respectively). With a population of about 14,000, Pierre is the second smallest state capital in the United States. Of the ten largest cities
South Dakota Highway 21 was completely concurrent with US 81, which was also established at this time. This concurrency extended from the Nebraska state line to the North Dakota state line. By 1935, all of SD 21 was decommissioned except for its current alignment. South Dakota Highway 21 South Dakota Highway 21 (SD 21) is a state highway in the eastern part of the U.S. state of South Dakota. It connects Lake Norden and Hayti, completely within the south-central part of Hamlin County. SD 21 originally extended from the Nebraska state line to the North Dakota state line, completely concurrent with U.S. Route 81