The Territory of Indiana was an organized incorporated territory of the United States that existed from July 4, 1800, until December 11, 1816, when the remaining southern portion of the territory was admitted to the Union as the state of Indiana.
The Indiana Territory was created by an Act of Congress and signed into law by President John Adams on May 7, 1800, effective on July 4. It was the first new territory created from lands of the Northwest Territory, which had been organized in 1787 by the Northwest Ordinance. The territory originally contained approximately 259,824 square miles (672,940 km2) of land, but twice decreased in size as it was further subdivided into new territories (Michigan Territory and Illinois Territory).
The territory was first governed by William Henry Harrison who oversaw the negotiation with the native inhabitants to open large parts of the territory to settlement. In 1810 a popularly elected government was established as the territory continued to grow in population and develop a very basic road network, government, and education system. At the outbreak of Tecumseh's War, the territory was on the front line of battle and Harrison led a military force in the opening hostilities at the Battle of Tippecanoe, and then in the subsequent invasion of Canada during the War of 1812. Thomas Posey was appointed to the vacant governorship, but the opposition party, led by Congressman Jonathan Jennings, had dominance in the territorial affairs for its remaining years and began pressing for statehood. In June 1816, a constitutional convention was held and a state government was formed. The territory was dissolved on December 11, 1816, by an act of Congress granting statehood to Indiana.
The original boundaries of the Indiana Territory included the area of the Northwest Territory west of a line running from the bank opposite the mouth of the Kentucky River northeast to Fort Recovery, and from there due northward along a line approximately 84 deg 45 min W longitude. The territory initially included most of present-day Indiana and all of present-day Illinois, and Wisconsin, as well as fragments of three other states: the part of Minnesota east of the Mississippi River, almost all of the Upper Peninsula of present-day Michigan and the western half of the Lower Peninsula, and finally, a narrow strip of present-day Ohio lying to the north and west of Fort Recovery. This latter parcel became part of the state of Ohio when it was admitted to the Union in 1803. At the same time in 1803, the southeast boundary shifted to the mouth of the Great Miami River from its former location at the point opposite the mouth of the Kentucky River. The eastern part of Michigan was added to the Indiana Territory at that time. The area of the Indiana Territory was reduced in 1805 by the creation of the Michigan Territory, and in 1809 by the creation of the Illinois Territory.