1. In 1889, South Dakota became the 40th state in the United States. January 20 marks the anniversary of South Dakota's statehood.

2. On January 20, 1925, the South Dakota legislature passed a bill legalizing the teaching of evolution in public schools. This was a controversial topic at the time, and the bill's passage made South Dakota one of the first states in the country to allow the teaching of evolution in schools.

3. In 1981, Ronald Reagan was inaugurated as the 40th President of the United States. This was a significant day for many South Dakotans, as Reagan was a popular political figure in the state.

4. On January 20, 1993, Bill Clinton was inaugurated as the 42nd President of the United States. Clinton's presidency had a significant impact on South Dakota, particularly in areas like healthcare and education.

5. In 2021, January 20 marked the inauguration of Joe Biden as the 46th President of the United States. Biden's presidency is expected to have a significant impact on South Dakota and the rest of the country, particularly in terms of healthcare, the economy, and the environment.