Ozark County is named for the oldest mountain range in the country, the Ozarks- the only country to wear that name. Two theories explain the origin of the name Ozark. One holds that it came from the French for the "Place of the Arkansas" (indians) or Aux-Ark. Another says it is derived from the French for the "Bluffs on the Bends"(of the white river), also Aux-Arcs.Ozark County lies in the old New Madrid District, one of the five governmental units formed by the Spanish by 1789 along the mississippi river. When the Americans took control of the regions they kept the county's in place and divided the Louisiana Purchase into the Territory of Orleans and the District of Louisiana. The territory of Orleans reached from what is now the southern border of Arkansas to the Gulf of Mexico, and the District of Louisiana included what are now the states of Missouri and Arkansas.

The first settlers, hardy pioneers hailing mainly from the South, arrived in the 1830's and staked claims in the rich river bottoms of the Ozark Wilderness. They built log cabins, broke soil for the crops and began to tame the land. Ozark County was organized in 1841 with Rockbridge as the County seat. In 1857 the seat was shifted to a more central location Gainesville.

In 1943, Lake Norfork was formed by a dam on the White River's North Fok in Arkansas, with arms in Ozark County. In 1951, another dam on the White River impounded Bull Shoals Lake, named for the Bull Mountain and the river shoals, which also reached well into Ozark County.