Sioux, or Dakota, Indians, a large and powerful tribe of Indians, who were found by the French, in 1640, near the headwaters of the Mississippi River. The Algonquiens called them Nadowessioux, whence they came to be called Sioux. They occupied the vast domain extending from the Arkansas River, in the south, to the western tributary of Lake Winnipeg, in the north, and westward to the eastern slopes of the Rocky Mountains. They have been classed into four grand divisions - namely, the Winnebagoes, who inhabited the country between Lake Michigan as the Mississippi, among the Algonquians; the Assiniboines, or Sioux proper (the most northerly of the nation) ; the Minnetaree group, in Minnesota; and the Southern Sioux, who dwelt in the country between the Arkansas and Platte rivers, and whose hunting-grounds extended to the Rocky Mountains. In 1679 Jean Duluth, a French officer, set up the Gallic standard among them near Lake St. Peter, and next year he rescued from them Father Hennepin, who first explored the upper Mississippi. The French took formal possession of the country in 1685, when they were divided into seven eastern and nine western tribes. In wars with the French and other Indians, they were pushed down the Mississippi, and, driving off the inhabitants of the buffalo plains, took possession.