1. On April 4, 1948, the Union Stock Yards in Chicago officially closed. The stock yards were once the largest livestock market in the world, and played a significant role in the growth of the city of Chicago.

2. In 1968, civil rights leader Martin Luther King Jr. was assassinated in Memphis, Tennessee. In Chicago, the news of King's death led to riots and protests in the city's West Side and Near North neighborhoods.

3. April 4, 1972 marked the first day of operation for the Chicago Board Options Exchange (CBOE), the first exchange in the world that allowed standardized options trading. Today, the CBOE is one of the largest options exchanges in the world.

4. On April 4, 1989, a natural gas explosion in a building on the south side of Chicago killed 21 people and injured over 50. The blast was so powerful that it caused several nearby buildings to collapse.

5. In 2011, the Chicago Cubs played their first regular season game at Wrigley Field with a new video scoreboard. The historic ballpark had never featured a video scoreboard before, and the addition was met with mixed reactions from fans.