Potosi is a city in Washington County, Missouri, United States. Potosi is seventy-two miles southwest of St. Louis. The population was 2,660 at the 2010 census. It is the county seat of Washington County. The city was founded sometime between 1760 and 1780 as "Mine à Breton" or Mine au Breton, and later renamed by Moses Austin for the Bolivian silver-mining city of Potosí.
According to the United States Census Bureau, the city has a total area of 2.33 square miles (6.03 km2), all land.
A lead mining settlement at this spot, "Mine à Breton" or Mine au Breton, was founded between 1760 and 1780 by Francis Azor, of Brittany, France. Moses Austin came here in 1798 with his family, including his son Stephen F. Austin. Moses obtained a grant of 7,153 arpents of land from the Spanish Empire and started large-scale mining operations, building his town to support it. Moses named the town after Potosí in Bolivia, which was famous for its vast silver mines.