Farmington is a city in St. Francois County located about 75 miles (121 km) southwest of St. Louis in the Lead Belt region in Missouri. As of the 2020 census, the population was 18,217. It is the county seat of St. Francois County. Farmington was established in 1822 as Murphy's Settlement, named for William Murphy of Kentucky, who first visited the site in 1798. When St. Francois County was organized, the town was briefly called St. Francois Court House and later renamed to Farmington.

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.