The following important events in the history of South Dakota affected political boundaries, record keeping, and family movements.

1803	The United States acquired the region from France as part of the Louisiana Purchase. Between 1803 and 1858, the area was the domain of the Dakota Sioux Indians and fur traders from St. Louis.
1820-1840	U.S. military expeditions were sent to the area in the 1820s, and Army posts were established in the 1850s. At various times, the area was part of the territories of Missouri, Michigan, Wisconsin, Iowa, Minnesota, and Nebraska.
1858	Yankton Sioux Indians ceded their claim to southeastern Dakota to the United States. Permanent white settlements were established at Yankton and Vermillion. For several years, settlement was confined to the area between the Big Sioux and the Missouri rivers.
1861	Congress created Dakota Territory, which included all of present-day North and South Dakota, Montana, and northern Wyoming. The first counties were established in southeastern Dakota in 1862. The creation of Montana Territory in 1864 and Wyoming Territory in 1868 reduced Dakota Territory to the area included in the two Dakotas of today.
1875	Discovery of gold in the Black Hills led to the opening of that area to white settlement in 1876. About 20,000 people came to South Dakota, but many left after a few months or years. The peak year of the gold rush was 1877.
1878-1887	The building of railroads in the region stimulated the great Dakota land boom, bringing settlers to most of the area east of the Missouri River.
1889	South Dakota was separated from North Dakota and became a state.
1900-1910	As railroads reached the western part of the state, the last land boom brought thousands of homesteaders.