Original: The Territory of Michigan was an organized incorporated territory of the United States that existed from June 30, 1805, until January 26, 1837, when the final extent of the territory was admitted to the Union as the State of Michigan.
Simplified: Michigan Territory was a territory of the United States in the early 19th century, between June 30, 1805 and January 26, 1837, when it became Michigan, the 26th state of the Union.