1. In 1876, a band of Oglala Lakota led by Chief Crazy Horse defeated the United States Army at the Battle of the Little Bighorn in Montana. This event had a significant impact on the history of the Black Hills region of South Dakota.

2. The Homestead Act of 1862, which provided free land to settlers willing to farm it for five years, went into effect on August 26. This law led to a significant increase in settlement in South Dakota and other western states.

3. In 1920, South Dakota became the first state to grant women the right to vote by a state referendum. This was a significant milestone in the women's suffrage movement.

4. On August 26, 1937, President Franklin D. Roosevelt visited Pierre, South Dakota, where he dedicated the Oahe Dam on the Missouri River. The dam provided critical hydroelectric power and irrigation for the region.

5. On August 26, 1972, a major mining disaster occurred in Lead, South Dakota. A fire broke out in the Homestake Mine, killing six miners and trapping others underground for over 24 hours. The disaster had a significant impact on the mining industry and safety regulations in the state.