Oregon County is a county located in the southern portion of the U.S. state of Missouri. As of the 2020 census, the population was 8,635. Its county seat is Alton. The county was officially organized on February 14, 1845, and was named for the Oregon Territory in the northwestern United States. Eleven Point State Park is under development east of Alton, Missouri that includes 6 miles of Eleven Point River frontage. Grand Gulf State Park is just west of Thayer that includes a collapsed karst canyon.