St. Francois County is a county in the Lead Belt region in the U.S. state of Missouri. At the 2020 census, the population was 66,922. The largest city and county seat is Farmington. The county was officially organized on December 19, 1821. It was named after the St. Francis River. The origin of the river's name is unclear. It may refer to St. Francis of Assisi. Another possibility is that Jacques Marquette, a Jesuit who explored the region in 1673, named the river for the Jesuit missionary Francis Xavier; Marquette had spent some time at the mission of St. François Xavier before his voyage and, as a Jesuit, was unlikely to have given the river a name honoring the Franciscans. Collected from Wikipedia.