Dakota Territory was the name of an organized territory of the United States that existed from 1861 to 1889. The territory consisted of the northernmost part of the land acquired in the Louisiana Purchase of the United States.

Most of Dakota Territory was formerly part of the Minnesota and Nebraska territories. When Minnesota became a state in 1858, the leftover area east of the Missouri River 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. However, it wasn't until three years later when soon-to-be-President Abraham Lincoln's cousin-in-law, J.B.S. Todd, personally lobbied for territory status that Washington formally created Dakota Territory.

It became a historic, organized territory on March 2, 1861. Upon creation, the territory of Dakota Territory included much of present-day Montana and Wyoming; by 1868, creation of new territories reduced Dakota Territory to the present boundaries of the Dakotas.

The territorial capital was Yankton from 1861 until 1883, when it was moved to Bismarck. Dakota Territory was divided into the states of North Dakota and South Dakota on November 2, 1889. The admission of two states, as opposed to one, was done for a number of reasons. The two centers of population in the territory were in the northeast and southeast corners of the territory, several hundred miles away from each other. On a national level, there was pressure from the Republican Party to admit the two states rather than one to add political power in the Senate.