The Territory of Dakota was an organized incorporated territory of the United States that existed from March 2, 1861, until November 2, 1889, when the final extent of the reduced territory was split and admitted to the Union as the states of North and South Dakota.

The Dakota Territory consisted of the northernmost part of the land acquired in the Louisiana Purchase of the United States. The name refers to the Dakota branch of the Sioux tribes which occupied the area at the time. Most of Dakota Territory was formerly part of the Minnesota and Nebraska territories. When Minnesota became a state in 1858, the leftover area between the Missouri River and Minnesota's western boundary fell unorganized. When the Yankton Treaty was signed later that year, ceding much of what had been Lakota land to the U.S. Government, early settlers formed an unofficial provisional government and unsuccessfully lobbied for United States territory status. Three years later soon-to-be-President Abraham Lincoln's cousin-in-law, J.B.S. Todd, personally lobbied for territory status and Washington formally created Dakota Territory.