On June 15, several notable historical events have occurred in Missouri, based on available records:
- 1820: Missouri's first constitutional convention convened in St. Louis to draft a state constitution, a key step toward Missouri's admission to the Union as a state in 1821.
- 1861: During the Civil War, Union General Nathaniel Lyon captured Jefferson City, Missouri's capital, without resistance, securing control of the state government for the Union.
- 1904: The St. Louis World's Fair, officially known as the Louisiana Purchase Exposition, was in full swing on June 15, showcasing Missouri's role as a cultural and economic hub. While no specific event is tied to this exact date, the fair itself was a significant moment in Missouri's history, drawing millions to St. Louis.