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

• 1804: The Lewis and Clark Expedition was near present-day Sioux City, Iowa, across from Missouri’s Atchison County, on or around August 21. They were recovering from the death of Sergeant Charles Floyd the previous day and continued documenting the region’s geography, advancing their exploration of the Louisiana Purchase.
• 1838: During the Mormon War in Missouri, tensions remained high. On or around August 21, non-Mormon vigilantes in Daviess and Carroll Counties continued their campaign against Mormon settlers, with skirmishes escalating the conflict that led to the Mormon expulsion order later in 1838.
• 1861: During the Civil War, the aftermath of the Battle of Wilson’s Creek (August 10) was ongoing in Missouri. On August 21, Union forces were regrouping after their retreat from Springfield, while Confederate forces maintained control in southwest Missouri, underscoring Missouri’s critical role in the conflict.
• 1870: The Kansas City Stockyards expanded operations around August 21, reinforcing Kansas City’s position as a major livestock trading hub and boosting Missouri’s agricultural economy.
• 1904: The St. Louis World’s Fair, or Louisiana Purchase Exposition, was ongoing, with August 21 featuring international cultural exhibits and early Olympic events, highlighting Missouri’s global prominence.
• 1964: The St. Louis Cardinals played a notable game against the New York Mets at Busch Stadium on August 21, with Lou Brock stealing two bases and contributing to a Cardinals victory, reinforcing Missouri’s baseball legacy during their World Series-winning season.