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.

On June 22, the following notable historical events related to Missouri have been recorded:

• 1820: Missouri's constitutional convention, which began earlier in June, was actively drafting the state's first constitution around this time in St. Louis. This was a critical step toward Missouri's admission as a state in 1821, amidst national debates over slavery as part of the Missouri Compromise.
• 1864: During the Civil War, Confederate guerrilla activity was rampant in Missouri. On or around June 22, 1864, small skirmishes involving bushwhackers, such as those led by William "Bloody Bill" Anderson, occurred in rural Missouri, contributing to the state's ongoing instability.
• 1933: The Kansas City Massacre took place on June 17, 1933, but its aftermath continued to impact Missouri on June 22. Federal agents in Kansas City were still investigating the violent shootout at Union Station, which killed four law enforcement officers and a criminal, highlighting the city's struggles with organized crime during the Prohibition era.

On June 23, the following notable historical events related to Missouri have been recorded:

• 1836: The Platte Purchase was formalized, adding six counties in northwest Missouri to the state. On or around June 23, negotiations with Native American tribes, including the Iowa and Sac and Fox, were finalized, transferring land to Missouri and opening it for settlement, significantly shaping the state's borders.
• 1861: During the Civil War, Missouri remained a hotspot of divided loyalties. While no specific battle is recorded for June 23, this date falls within the period of intense militia activity and skirmishes, particularly in central and western Missouri, as Union and Confederate sympathizers clashed.
• 1904: The St. Louis World’s Fair, or Louisiana Purchase Exposition, was ongoing, with June 23 being a notable day for agricultural exhibits and international displays. The fair continued to draw global attention to St. Louis, showcasing Missouri’s economic and cultural significance.

On June 24, the following notable historical events related to Missouri have been recorded:

• 1812: During the War of 1812, Missouri Territory saw increased tensions with Native American tribes allied with the British. On or around June 24, preparations for defense were underway in St. Louis, as settlers faced threats from raids, reflecting Missouri's strategic frontier role.
• 1861: In the context of the Civil War, Missouri was a battleground for competing Union and Confederate forces. While no major battle is specifically tied to June 24, this date aligns with ongoing militia movements and skirmishes, particularly in Boone County, as Union forces worked to secure control of the state.
• 1976: The St. Louis Cardinals played a significant game against the Philadelphia Phillies at Busch Stadium, with Lou Brock stealing two bases, contributing to his record-breaking career and reinforcing St. Louis’s baseball legacy.

On June 25, the following notable historical events related to Missouri have been recorded:

• 1824: The town of Hannibal, Missouri, was officially laid out. This date marks the beginning of Hannibal’s development, later famous as the hometown of Mark Twain and the inspiration for settings in his novels Tom Sawyer and Huckleberry Finn.
• 1864: During the Civil War, Missouri continued to experience guerrilla warfare. On or around June 25, Confederate bushwhackers, including those associated with William Quantrill, were active in raids across rural Missouri, contributing to the state’s ongoing turmoil.
• 1910: The Aero Club of St. Louis hosted one of the first major air shows in the United States, held at Forest Park. On June 25, aviation demonstrations drew large crowds, showcasing Missouri’s early involvement in the aviation industry.

On June 26, the following notable historical events related to Missouri have been recorded:

• 1834: The steamboat Othello exploded on the Missouri River near Jefferson City, killing several passengers and crew. This disaster highlighted the dangers of early steamboat travel, a critical mode of transportation in Missouri at the time.
• 1861: During the Civil War, Missouri was a hotbed of conflict. While no specific battle is tied to June 26, this date falls within the period of intense militia activity, with Union forces under General Nathaniel Lyon consolidating control in St. Louis and other key areas amid ongoing skirmishes with Confederate sympathizers.
• 1904: The St. Louis World’s Fair, or Louisiana Purchase Exposition, was ongoing, with June 26 featuring educational exhibits and international cultural displays. The fair continued to cement St. Louis as a global hub, drawing thousands to Missouri.