National South Dakota Day Date in the current year: April 26, 2025

South Dakota is a landlocked state in the Midwestern United States, bordered by North Dakota, Minnesota, Iowa, Nebraska, Wyoming, and Montana. Geographically, it is part of the Great Plains.

North and South Dakota, which once formed a single Dakota territory, were named after an ethnolinguistic group within the Native American Sioux people. The word “Dakota” means “ally” or “friend” in the Dakota language. South Dakota’s official nickname is the Mount Rushmore State in honor of the Mount Rushmore National Memorial in the Black Hills near Keystone.

The area that is now South Dakota has been inhabited for thousands of years. Among the first Native Americans to arrive in the area were the Arikara, Cheyenne, and Ioway. The Sioux, who would eventually dominate much of South Dakota, arrived in the region sometime in the late 16th or early 17th century.

The first European country to claim what is now South Dakota was France in the late 17th century. However, most French explorers did not venture deep into its territory. In 1762, France and Spain signed the secret Treaty of Fontainbleau, by which France ceded to Spain its lands in North America west of the Mississippi River. However, the Spanish never established actual control over the region.

In 1800, Spain returned Louisiana to France in exchange for territories in Tuscany through another secret agreement, the Third Treaty of San Ildefonso. Three years later, Napoleon sold Louisiana to the United States; the vast territory included nearly all of present-day South Dakota.

After the Louisiana Purchase President Thomas Jefferson commissioned Meriwether Lewis and William Clark to explore the newly acquired region; their expedition reached what is now South Dakota in August 1804. The first American settlement in South Dakota was Fort Pierre, established in 1817 as a fur-trading post.

The Dakota Territory was officially created on March 2, 1861. It included all of present-day North and South Dakota, most of present-day Montana and Wyoming, and a small part of present-day Nebraska. When the American Civil War broke out, the Dakota Territory was not directly involved, but it did supply some soldiers to the Union Army.

Since there had always been tensions between the northern and southern parts of the Dakota Territory, they were admitted to the Union as separate states, alongside Montana and Washington, according to the Enabling Act of 1889. North and South Dakota officially joined the Union on November 2, 1889.

In 2017, National Day Calendar introduced the National State Days project to honor the history and culture of each U.S. state in the order in which they entered the Union. While North and South Dakota were admitted together and share the same statehood anniversary, each has its own holiday in the National State Days project: North Dakota Day is celebrated on April 19, and South Dakota Day is celebrated on April 26.