1. The Illinois Constitution was adopted on December 5, 1818, making Illinois the 21st state to join the Union. The constitution established Illinois as a free state, prohibited slavery, and created the Illinois General Assembly.

2. On December 5, 1927, the first underground parking garage in the United States opened in Chicago. The garage was located beneath the Civic Opera Building and could hold over 600 cars.

3. The landmark case of Village of Euclid, Ohio v. Ambler Realty Co. was decided by the U.S. Supreme Court on December 5, 1926. The case upheld a zoning ordinance that regulated land use and set a precedent for future zoning laws.

4. University of Illinois scientist John Bardeen, along with Walter Brattain and William Shockley, successfully demonstrated the first transistor on December 5, 1947. This breakthrough in electronics revolutionized the field and led to the development of modern computers.

5. On December 5, 2018, Julián Castro, former Secretary of Housing and Urban Development under President Obama, hosted a town hall meeting at the University of Illinois at Chicago as part of his presidential campaign to seek the Democratic nomination for the 2020 presidential election.