is a county located in the southern portion of the U.S. state of Missouri. As of the 2010 census, the population was 9,723. The largest city and county seat is Gainesville. The county was organized as Ozark County, named after the Ozark Mountains, on January 29, 1841. It was renamed Decatur County, after Commodore Stephen Decatur, from 1843 to 1845, after which the name Ozark County was restored.
According to the U.S. Census Bureau, the county has a total area of 755 square miles (1,960 km2), of which 745 square miles (1,930 km2) is land and 10 square miles (26 km2) (1.4%) is water. Arkansas is located to the south of Ozark County.