On August 12, the following notable historical events related to Missouri have been recorded:

• 1804: The Lewis and Clark Expedition was near present-day Omaha, Nebraska, across from Missouri’s Atchison County, on or around August 12. They continued documenting the region’s wildlife and interactions with Native American tribes, advancing their exploration of the Louisiana Purchase.
• 1838: During the Mormon War in Missouri, tensions escalated further. On or around August 12, non-Mormon vigilantes in Daviess and Carroll Counties intensified their campaign against Mormon settlers, with increased skirmishes contributing to 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) continued in Missouri. On August 12, Union forces were retreating from Springfield, while Confederate forces pursued, reinforcing Missouri’s central role in the conflict’s western theater.
• 1870: The Kansas City Stockyards expanded operations around August 12, solidifying 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 12 featuring international agricultural exhibits and early Olympic events, highlighting Missouri’s global cultural and economic prominence.
• 1964: The St. Louis Cardinals played a significant game against the Chicago Cubs at Busch Stadium on August 12, with Lou Brock stealing two bases and contributing to a Cardinals victory, reinforcing Missouri’s baseball legacy during their World Series-winning season.