Map of South Dakota

South Dakota ( də-KOH-tə; Dakota: Dakȟóta itókaga, pronounced [daˈkˣota iˈtokaga]) is a landlocked state in the North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Dakota Sioux tribe, which comprises a large portion of the population and has historically dominated the territory. South Dakota is the 17th-largest by area, the fifth-least populous, and the fifth-least densely populated of the 50 United States. Pierre is the state capital, and Sioux Falls, with a population of about 213,900, is the most populous city. The Missouri River bisects the state into two geographically and socially distinct halves colloquially known as "East River" and "West River". South Dakota is bordered by North Dakota to the north, Minnesota to the east, Iowa to the southeast, Nebraska to the south, Wyoming to the west, and Montana to the northwest.

Humans have inhabited the area for several millennia, with the Sioux becoming dominant by the early 19th century. In the late 19th century, European-American settlement intensified after a gold rush in the Black Hills and the construction of railroads from the east. Encroaching miners and settlers triggered a number of Indian wars, ending with the Wounded Knee Massacre in 1890. As the southern part of the former Dakota Territory, South Dakota became a state on November 2, 1889, simultaneously with North Dakota. They are the 39th and 40th states admitted to the union; President Benjamin Harrison shuffled the statehood papers before signing them so that no one could tell which became a state first.

Major events in the 20th century included the Dust Bowl and Great Depression, increased federal spending during the 1940s and 1950s for agriculture and defense, and the industrialization of agriculture, which has reduced family farming. Eastern South Dakota is home to most of its population, and a variety of crops grow in the area's fertile soil.