Timeline of Missouri History: 1800-1820
| 1800 | Moses Austin made the first sheet lead and cannonballs manufactured in Missouri | |
| 1800 | Spain returned the Louisiana Territory to France (Oct. 30) |  Fort Osage |
| 1803 | The Louisiana Purchase was signed (Apr. 30) | |
| 1804 | The Lewis and Clark Expedition set out from St. Louis (May 14) | |
| 1805 | The Territory of Louisiana was established; the seat of government was St. Louis (Mar. 3) | |
| 1808 | The city of Ste. Genevieve was incorporated (June 18) | |
| 1808 | Joseph Charless founded the first newspaper in Missouri, the "Missouri Gazette" | |
| 1808 | Fort Osage was established on the Missouri River | |
| 1809 | The Missouri Fur Company was organized in St. Louis. The abundance of animal pelts in the Mississippi Valley region played a key role in the development of the Upper Louisiana territory. Prominent members of the Company included fur trader Manuel Lisa, Auguste and Pierre Chouteau, and William Clark | |
| 1811 | The first shocks of the New Madrid earthquakes, the worst in US history, occurred (Dec. 16) | |
| 1812 | A portion of the Territory of Louisiana became the Territory of Missouri (June 4) | |
| 1812 | The first general assembly of the Territory of Missouri met (Oct. 1); the five original counties were organized: Cape Girardeau, New Madrid, St. Charles, St. Louis, and Ste. Genevieve | |
| 1816 | Mid-Missouri’s first circuit court opened at Cole’s Fort (July 8) | |
| 1817 | The steamboat Zebulon M. Pike reached St. Louis, the first steamboat to navigate the Mississippi River above the mouth of the Ohio River (Aug. 2) | |
| 1818 | The Speaker of the U.S. House of Representatives presented the first petition to Congress from Missouri requesting statehood (Jan. 8) | |