1. The first US post office in South Dakota was established on May 10, 1861. According to historical records, the first postmaster in the territory was A.H. Curtis, serving the community of Vermillion.

2. In 1881, May 10 saw the opening of the first railroad line to Rapid City, South Dakota. This landmark event marked the beginning of the city's rapid growth and development as a transportation hub for the region.

3. On May 10, 1933, South Dakota became the first state in the US to repeal its prohibition laws. The repeal of these laws, which had been in place since 1920, allowed for the legal sale and consumption of alcohol in the state once again.

4. In 1943, May 10 marked the beginning of the largest war games exercise ever conducted in South Dakota. The exercise, known as Operation Dakotan, involved over 16,000 soldiers and was designed to prepare troops for combat in the European theater of World War II.

5. On May 10, 1972, South Dakota's Badlands National Park was officially dedicated. The park, known for its striking geological formations and diverse wildlife, attracts over a million visitors each year and is one of the state's most popular tourist destinations.