September 21 is an important date in the history of Missouri, as it marks several significant events that have shaped the state's culture, politics, and society. Here are five interesting facts about September 21 in Missouri history:

1. Missouri became a state on September 21, 1820. After several years of negotiations and compromises over the Missouri Territory's admission to the Union, Congress finally passed the Missouri Compromise, which allowed Missouri to join as a slave state in exchange for Maine being admitted as a free state.

2. On September 21, 1935, the first meeting of the Ozark Folk Music Festival was held in Mountain View, Missouri. The festival is now the longest-running folk music festival in the United States and continues to attract thousands of visitors every year.

3. September 21, 1981, marked the opening of the Mark Twain Museum in Hannibal, Missouri. The museum is dedicated to the life and legacy of author Samuel Clemens, also known as Mark Twain, who spent much of his childhood in Hannibal and drew inspiration from the town in his writing.

4. On September 21, 1990, the City Museum opened in St. Louis, Missouri. Created by artist Bob Cassilly and his team of designers and builders, the museum is a unique attraction that features art installations, exhibits, and interactive experiences made from repurposed industrial materials.

5. September 21, 2017, was the first day of the second annual Roots N Blues N BBQ Festival in Columbia, Missouri. The festival celebrates the roots of American music, including blues, folk, and country, and features a lineup of renowned musicians and BBQ vendors from around the country.