Missouri, the twenty-fourth State, was admitted to the Union, August 10, 1821. Its name is derived from its principal river, and means "Muddy water". Its oldest town, St. Genevieve, was founded in 1755. St. Louis was settled nine years after, but was not incorporated as a town until 1809; its first newspaper was published in 1808, and the first steamboat arrived at its wharf in 1817. The District of Louisiana was organized as Louisiana Territory in 1805, with St. Louis as its capital. When Louisiana became a State, the name of the Territory was changed to Missouri.
Source: Barnes's Historical Series, A Brief History of the United States, by Joel Dorman Steele, Ph. D., F.G.S. and Esther Baker Steele, Lit. D., c. 1900, p. 204.