Which U.S. state was the 24th to join the Union?

Missouri was the 24th U.S. state to join the Union, entering in 1821.

Missouri’s admission followed a difficult national debate over slavery’s expansion into western territories. The Missouri Compromise of 1820 allowed Missouri to enter as a slave state while Maine entered as a free state, preserving the political balance between free and slave states in the Senate. The compromise also restricted slavery in much of the remaining Louisiana Purchase north of latitude 36°30′.

Missouri formally became a state on August 10, 1821. It was the first state located entirely west of the Mississippi River to join the Union. Saint Charles served temporarily as the state capital before Jefferson City assumed that role in 1826.

A frequent mix-up is placing Arkansas or Michigan at number 24. Arkansas became the 25th state in 1836, while Michigan became the 26th in 1837. Florida joined later, as the 27th state, in 1845.