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. A band of peaceful Onsaga-Osage Native Americans were slaughtered in 1801 and their lands captured by settlers in the infamous Battle of Red Grass Hill. Twelve pioneers were injured while 260 Native Americans were reportedly killed in battle, wounded, or executed shortly thereafter. A marker, bearing the site of the battle, was a prominent display until 1951 when it was stolen by vandals.