South Dakota is bordered by the states of 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). The state is bisected by the Missouri River, dividing South Dakota into two geographically and socially distinct halves, known to residents as "East River" and "West River".

Eastern South Dakota is home to most of the state's population, and the area's fertile soil is used to grow a variety of crops. West of the Missouri, ranching is the predominant agricultural activity, and the economy is more dependent on tourism and defense spending. Most of the Native American reservations are in West River. The Black Hills, a group of low pine-covered mountains sacred to the Sioux, are in the southwest part of the state. Mount Rushmore, a major tourist destination, is there. South Dakota has a temperate continental climate, with four distinct seasons and precipitation ranging from moderate in the east to semi-arid in the west. The state's ecology features species typical of a North American grassland biome.

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. Key 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 an industrialization of agriculture that has reduced family farming.

While several Democratic senators have represented South Dakota for multiple terms at the federal level, the state government is largely controlled by the Republican Party, whose nominees have carried South Dakota in each of the last 13 presidential elections. Historically dominated by an agricultural economy and a rural lifestyle, South Dakota has recently sought to diversify its economy in areas to attract and retain residents. South Dakota's history and rural character still strongly influence the state's culture.