The U.S. Congress created the Michigan Territory from the northernmost portion of the Indiana Territory on January 11, 1805. It originally comprised all of the current state of Michigan west of Lake Michigan and most of the current state east of the lake. In 1818, following the admission of Indiana and Illinois as states, the Michigan Territory extended further west, incorporating the current state of Wisconsin and portions of Minnesota, as well as the remainder of the current state of Michigan. It expanded again in 1834 to absorb the remainder of modern Minnesota, as well as Iowa, and portions of North and South Dakota. As Michigan neared statehood in 1836, the federal government split the territory, designating all but the current state of Michigan as the Wisconsin Territory. The territory officially ceased to exist when Michigan achieved statehood on January 26, 1837. Detroit was the territorial capital.
"An Act to Divide the Indiana Territory into Two Separate Governments," 11 January 1805, Statutes at Large of the United States 2 (1845):309-10; "An Act to Enable the People of the Illinois Territory to Form a Constitution and State Government, and for the Admission of Such State into the Union on an Equal Footing with the Original States," 18 April 1818, Statutes at Large of the United States 3 (1846):431; "An Act to Attach the Territory of the United States West of the Mississippi River, and North of the State of Missouri, to the Territory of Michigan," 28 June 1834, Statutes at Large of the United States 4 (1846):701; "An Act Establishing the Territorial Government of Wisconsin," 20 April 1836, Statutes at Large of the United States 5 (1856):10-11; "An Act to Admit the State of Michigan into the Union, Upon an Equal Footing with the Original States," 26 January 1837, Statutes at Large of the United States 5 (1856):144; Alec R. Gilpin, The Territory of Michigan, [1805-1837] (East Lansing: Michigan State University Press, 1970).