1. On April 18, 1862, the First Dakota Cavalry was organized in Dakota Territory. This regiment played a vital role in protecting settlers from Native American attacks during the Indian Wars.

2. In 1881, the first issue of the Daily Deadwood Pioneer-Times newspaper was published on April 18th. This newspaper offered news coverage of the booming town of Deadwood, which served as a center for gold mining in the Black Hills.

3. On April 18, 1936, the Oahe Dam was completed on the Missouri River in central South Dakota. This massive dam created Lake Oahe, which is one of the largest reservoirs in the United States and a major source of hydroelectric power for the region.

4. In 1946, the South Dakota State Board of Education established South Dakota State University's Extension Service on April 18th. This service provided research-based information and educational resources to farmers, ranchers, and other residents in rural areas.

5. On April 18, 1986, the Badlands National Park Visitor Center was opened to the public in southwestern South Dakota. This modern facility provides visitors with information about the unique geology and ecology of the park's distinctive landscape.