On June 14, the following notable historical events related to Missouri have been recorded:

• 1804: The Lewis and Clark Expedition was in the St. Louis area on or around June 14, finalizing preparations for their journey up the Missouri River to explore the Louisiana Purchase. They were securing final supplies and coordinating with local traders, reinforcing Missouri’s role as the launch point for western exploration.
• 1820: Missouri’s constitutional convention, convened in St. Louis, was actively drafting the state’s first constitution around June 14. This was a critical step toward Missouri’s admission as a state in 1821, amidst national debates over slavery tied to the Missouri Compromise.
• 1861: During the Civil War, Missouri was a focal point of conflict. On June 14, Union General Nathaniel Lyon was mobilizing forces toward Jefferson City after the failed St. Louis Conference, preparing to capture the state capital to secure Missouri for the Union against Confederate sympathizers.
• 1876: The St. Louis-based Missouri Botanical Garden, founded by Henry Shaw, hosted a significant public exhibition around June 14, showcasing rare tropical plants and reinforcing its reputation as a leading botanical research center.
• 1904: The St. Louis World’s Fair, or Louisiana Purchase Exposition, was underway, with June 14 featuring early international scientific exhibits and cultural performances, highlighting Missouri’s prominence as a global hub.
• 1967: The St. Louis Cardinals played a notable game against the New York Mets at Busch Stadium on June 14, with Bob Gibson pitching a shutout and Orlando Cepeda hitting a key home run, contributing to their World Series-winning season and reinforcing Missouri’s baseball legacy.

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.