Washington County, MO
History
The French explorers Renault and La Motte entered the area of present day Potosi in 1722-23. However, no permanent settlements were made until 1763, when Francois Breton settled near Potosi and began to operate a mine bearing his name.At a time when Missouri was part of Louisiana and still a Spanish province, Moses Austin who was later prominent in early Texas history, was granted from the Spanish Commandant a square league of land and the lead mines discovered at a place called Mine A Burton near St. Genevieve in January of 1797. He also received the right to settle thirty families there from the United States. Austin created the first permanent settlement in Washington County, Missouri. He erected smelting furnaces, and developed the lead deposits.
Upper Louisiana, of which Missouri was a part, entered the United States in 1804 after President Thomas Jefferson's Louisiana Purchase and Washington County was officially organized on August 21, 1813, out of Ste. Genevieve County.
Source: Wikipedia and the website for Washington County, Missouri