Indiana Territory was an organized territory of the United States from 1800 to 1816, created by 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 (430,000 km²) of land. The territory ceased to exist when Indiana statehood was approved in 1816.
The territory was first governed by William Henry Harrison who oversaw the negotiation of treaties opening up the territory to settlement, the establishment of a popularly elected government, and the basic development of infrastructure. At the outbreak of Tecumseh's War the territory was on the front line of battle and Harrison led the territory's militia and regulars in 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 legislature dominated the territorial government for its remaining years. In June 1816 a constitutional convention was held and a state government was formed. The territory was dissolved on November 7, 1816, by an act of Congress granting statehood to Indiana.