1. Statehood Day: May 9, 1889, is a significant day in South Dakota history as it marks the day when South Dakota was admitted to the Union as the 40th state.

2. Mount Rushmore: On May 9, 1927, work began on Mount Rushmore, one of South Dakota's most famous landmarks. The sculpture features the faces of four U.S. Presidents: George Washington, Thomas Jefferson, Abraham Lincoln, and Theodore Roosevelt.

3. First Flight: On May 9, 1911, South Dakota's first airplane flight took place in Sioux Falls. John H. Rosenstein flew a biplane for three miles, reaching a speed of 45 miles per hour.

4. Homestake Gold Mine: On May 9, 1876, the Homestake Gold Mine in Lead, South Dakota, was founded. It was one of the richest and deepest gold mines in the world, producing over 40 million troy ounces of gold over its 125-year lifespan.

5. Crazy Horse Memorial: On May 9, 1947, sculptor Korczak Ziolkowski began working on the Crazy Horse Memorial in the Black Hills of South Dakota. The memorial honors the legendary Lakota warrior and leader, and when completed, it will be the largest mountain carving in the world.