The Jefferson County Courthouse is located at 300 2nd Street, Hillsboro, MO 63050; phone: 636-797-5555.
Jefferson County was organized December 8, 1818, from St. Louis and Ste. Genevieve counties and named for Thomas Jefferson, 3rd President of the United States. The first county seat was at Herculaneum. It was moved to land that would become Hillsboro in 1839. Hillsboro was incorporated in 1873.