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.

On June 16, several notable historical events have occurred in Missouri, based on available records:

• 1822: The first steamboat, the Western Engineer, arrived in St. Joseph, Missouri. Designed by Henry M. Shreve, it revolutionized transportation on the Missouri River, facilitating trade and settlement in the region.
• 1933: Missouri became the first U.S. state to enact a sales tax, set at one percent, to generate revenue during the Great Depression.

• 1967: The Gateway Arch in St. Louis was completed. Designed by Eero Saarinen, this 630-foot monument, the tallest arch in the world, commemorates St. Louis’ role as the “Gateway to the West.”

On June 17, the following notable historical events related to Missouri have been recorded:

• 1871: The Great Chicago Fire's aftermath indirectly impacted Missouri, as St. Louis became a key supplier of goods and materials for Chicago's reconstruction. While the fire itself occurred later, on June 17, 1871, St. Louis merchants were already positioning themselves as critical players in regional trade, a role solidified post-fire.
• 1969: The St. Louis Cardinals played a significant game at Busch Stadium, defeating the Pittsburgh Pirates. This victory was part of their 1960s dominance, showcasing St. Louis as a major sports hub.

On June 18, the following notable historical events related to Missouri have been recorded:

• 1812: The War of 1812 began with the U.S. declaration of war against Britain. Missouri, then a territory, played a role as a frontier region, with conflicts involving Native American tribes allied with the British, particularly in the St. Louis area.
• 1874: The St. Louis Browns, a precursor to the modern St. Louis Cardinals, played one of their earliest professional baseball games, marking the city's growing prominence in American sports.
• 1942: During World War II, the Weldon Spring Ordnance Works in St. Charles County, Missouri, began operations. This massive facility produced explosives, contributing significantly to the war effort.

On June 19, the following notable historical events related to Missouri have been recorded:

• 1861: During the Civil War, the Battle of Cole Camp occurred in Benton County, Missouri. Confederate sympathizers attacked a Union encampment, resulting in a Confederate victory. This skirmish was part of the early struggles for control of Missouri during the war.
• 1865: Juneteenth, marking the emancipation of enslaved African Americans, was celebrated in Missouri and other states. While the official announcement of emancipation in Texas occurred on June 19, 1865, Missouri had abolished slavery earlier that year on January 11, 1865, through a state ordinance. Celebrations of freedom on this date still resonated in Missouri communities.
• 1964: The Civil Rights Act of 1964 was under intense debate in the U.S. Senate, with Missouri Senator Thomas Eagleton playing a key role in supporting its passage. While the act was signed later, on July 2, discussions and negotiations on June 19 were pivotal, reflecting Missouri’s involvement in national civil rights advancements.

On June 20, the following notable historical events related to Missouri have been recorded:

• 1820: The Missouri Compromise, which balanced the admission of Missouri as a slave state with Maine as a free state, was a significant topic of discussion around this time, though not specifically finalized on June 20. On this date, Missouri's territorial leaders were actively preparing for statehood, with debates over slavery intensifying in St. Louis and beyond.
• 1863: During the Civil War, Confederate guerrillas, including those led by William Quantrill, were active in Missouri. While no major battle is recorded for June 20 specifically, skirmishes and raids were common in Missouri during this period, contributing to the state's volatile role in the conflict.
• 1904: The St. Louis World's Fair, or Louisiana Purchase Exposition, was ongoing, with June 20 being a notable day for exhibitions and cultural displays. The fair highlighted Missouri's economic and cultural prominence, attracting global attention to St. Louis.

On June 21, the following notable historical events related to Missouri have been recorded:

• 1818: The steamboat Independence became one of the first to navigate the Missouri River, reaching Franklin, Missouri, around this date. This marked a significant advancement in transportation and commerce for the Missouri Territory, boosting settlement and trade.
• 1861: During the Civil War, pro-Union and pro-Confederate factions in Missouri were engaged in ongoing tensions. While no specific battle occurred on June 21, this date falls within the period of the "Camp Jackson Affair" aftermath, where St. Louis was a focal point of conflict between Union forces and secessionist militias.
• 2004: The St. Louis Cardinals played a notable game against the Chicago Cubs at Busch Stadium, with Albert Pujols hitting a key home run, contributing to a Cardinals victory. This game was part of their successful 2004 season, which saw them reach the World Series.