South Dakota is bisected by the Missouri River, dividing the state into two socioeconomically distinct halves, known to residents as "West River" and "East River". Fertile soil in the eastern part of the state is used to grow a variety of crops, while ranching is the predominant agricultural activity in the west. The Black Hills, a group of low pine-covered mountains, is located in the southwest part of the state. The area is of great religious importance to local American Indian tribes. Mount Rushmore is a major state tourist destination in the Black Hills.
Historically dominated by an agricultural economy and a rural lifestyle, South Dakota has recently sought to diversify its economy to attract and retain residents. However, it is still largely rural and has the fifth-lowest population density among U.S. states. While several Democratic senators have represented South Dakota for multiple terms at the federal level, the state government is largely dominated by the Republican Party, which has carried South Dakota in the last eleven presidential elections.
According to the U.S. Census Bureau, as of 2006, South Dakota has an estimated population of 781,919, an increase of 27,075, or 3.6%, since the year 2000. 7.0% of South Dakota's population were reported as under 5, 24.9% under 18, and 14.2% were 65 or older. Females made up approximately 50.0% of the population. As of the 2000 census, South Dakota ranked fifth-lowest in the nation in both population and population density. The center of population of South Dakota is located in Buffalo County, in the unincorporated county seat of Gannvalley.
In 2005, the Census Bureau estimated that 88.5% of South Dakotans were White, 8.8% were American Indian or Alaskan Native, 2.1% were Hispanic (of any race), 0.8% were Black, 0.7% were Asian, and 2.1% belonged to more than one race. The five largest ancestry groups in South Dakota are: German (40.7%), Norwegian (15.3%), Irish (10.4%), Native American (8.3%), and English (7.1%). German-Americans are the largest ancestry group in most parts of the state, especially in the east, although there are also large Scandinavian populations in some counties. South Dakota has the nation's largest population of Hutterites, a communal Anabaptist group who emigrated from Europe in 1874.
American Indians, largely Lakota, Dakota, and Nakota (Sioux) are predominant in several counties. South Dakota has the third highest proportion of Native Americans of any state, behind Alaska and New Mexico. Five of the state's counties are wholly within Indian reservations. Living standards on many reservations are often very low when compared with the national average. The unemployment rate in Fort Thompson, on the Crow Creek Indian Reservation, is 70%, and 21% of households there lack plumbing or basic kitchen appliances. A 1995 study by the U.S. Census Bureau found that 58% of homes on the Pine Ridge Indian Reservation did not have a telephone.
As of the 2000 census, 1.90% of the population aged 5 or older speak German at home, while 1.51% speak Dakota, and 1.43% Spanish.
South Dakota, in common with other Great Plains states, has been experiencing a falling population in many rural areas over the last several decades, a phenomenon known as "rural flight". This trend has continued in recent years, with 30 of South Dakota's counties losing population between the 1990 and the 2000 census. During that time, nine counties experienced a population loss of greater than 10%, with Harding County, in the northwest corner of the state, losing nearly 19% of its population. Low birth rates and a lack of younger immigration has caused the median age of many of these counties to increase. In 24 counties, at least 20% of the population is over the age of 65, compared with a national rate of 12.5%.
The effect of rural flight has not been spread evenly through South Dakota, however. Although most rural counties and small towns have lost population, the Sioux Falls area, the larger counties along Interstate 29, the Black Hills, and many Indian reservations have all gained population. In fact, Lincoln County, near Sioux Falls, is the ninth-fastest growing county (by percentage) in the United States. The growth in these areas has compensated for losses in the rest of the state, and South Dakota's total population continues to increase steadily, albeit at a slower rate than the national average.
The largest denominations by number of adherents in 2000 were the Roman Catholic Church with 181,434 members; the Evangelical Lutheran Church in America (ELCA) with 121,871 members; and the United Methodist Church (UMC) with 37,280 members. (Both the ELCA and UMC are specific denominations within the broader terms 'Lutheran' and 'Methodist', respectively.) The results of a 2001 survey, in which South Dakotans were asked to identify their religion, include:
South Dakota has a total of 83,609 miles of highways, roads, and streets, along with 679 miles of interstate highways. Two major interstates pass through South Dakota: Interstate 90, which runs east and west; and Interstate 29, running north and south in the eastern portion of the state. The I-29 corridor features generally higher rates of population and economic growth than areas in eastern South Dakota that are further from the interstate. Also located in the state are the shorter interstates 190, a spur into central Rapid City, and 229, a loop around eastern and southern Sioux Falls. Several major U.S. highways pass through the state. U.S. routes 12, 14, 16, 18, and 212 travel east and west, while U.S. routes 81, 83, 85 and 281 run north and south.
South Dakota contains two National Scenic Byways. The Peter Norbeck National Scenic Byway is located in the Black Hills, while the Native American Scenic Byway runs along the Missouri River in the north-central part of the state. Other scenic byways include the Badlands Loop Scenic Byway, the Spearfish Canyon Scenic Byway, and the Wildlife Loop Road Scenic Byway.
Railroads have played an important role in South Dakota transportation since the mid-19th century. Some 4,420 miles (7,110 km) of railroad track were built in South Dakota during the late nineteenth and early twentieth centuries, but only 1,839 miles (2,960 km) are active. BNSF Railway is currently the largest railroad in South Dakota; the Dakota, Minnesota, and Eastern Railroad is the state's other major carrier. Rail transportation in the state is confined only to freight, however, as South Dakota is one of the few states without any Amtrak service.
South Dakota's largest commercial airports in terms of passenger traffic are the Sioux Falls Regional Airport and Rapid City Regional Airport. Northwest Airlines, Frontier Airlines, and Allegiant Airlines, as well as commuter airlines using the brand affiliation with major airlines serve the two largest airports. Several other cities in the state also have commercial air service, some of which is subsidized by the Essential Air Service program.