Northwest Territory
The Northwest Territory in the United States (also known as the Old Northwest) was formed after the American Revolutionary War, and was known formally as the Territory Northwest of the River Ohio. It was the initial post-colonial Territory of the United States and encompassed most of pre-war British colonial territory west of the Appalachian mountains north of the Ohio River. It included all the land west of Pennsylvania, northwest of the Ohio River and east of the Mississippi River below the Great Lakes. It spanned all or large parts of six eventual U.S. States (Ohio, Indiana, Illinois, Michigan, Wisconsin, and the northeastern part of Minnesota). It was created as a Territory by the Northwest Ordinance July 13, 1787, reduced to Ohio, eastern Michigan and a sliver of southeastern Indiana with the formation of Indiana Territory July 4, 1800, and ceased to exist March 1, 1803, when the southeastern portion of the territory was admitted to the Union as the state of Ohio, and the remainder attached to Indiana Territory.
Northwest Territory
At its inception the Territory was a vast wilderness sparsely populated by Indians including the Delaware, Miami, Potawatomi, Shawnee and others; there were only a handful of French colonial settlements, and Clarksville at Falls of the Ohio. At the territory's dissolution, there were dozens of towns and settlements, a few with thousands of settlers, mostly in Ohio chiefly along the Ohio and Miami Rivers and around the Great Lakes.
Northwest Ordinance
The Northwest Ordinance (formally An Ordinance for the Government of the Territory of the United States, North-West of the River Ohio, and also known as The Ordinance of 1787) enacted July 13, 1787, was an organic act of the Congress of the Confederation of the United States. It created the Northwest Territory, the first organized territory of the United States, from lands beyond the Appalachian Mountains, between British North America and the Great Lakes to the north and the Ohio River to the south. The upper Mississippi River formed the territory's western boundary. Pennsylvania was the eastern boundary.
Northwest Ordinance
In the Treaty of Paris (1783), which formally ended the American Revolutionary War, Great Britain yielded this region to the United States. However, the Confederation Congress faced numerous problems gaining control of the land; these included: the unsanctioned movement of American settlers into the Ohio Valley, violent confrontations with the region's indigenous peoples, the ongoing presence of the British Army which continued to occupy forts in the region, and an empty U.S. treasury. The ordinance superseded the Land Ordinance of 1784 (which declared that states would one day be formed within the region) and the Land Ordinance of 1785 (which described how the Confederation Congress would sell the land to private citizens). Designed to serve as a blueprint for the development and settlement of the region, what the 1787 ordinance lacked was a strong central government to implement it. This need was addressed shortly thereafter, when the new federal government came into existence in 1789. The 1st United States Congress reaffirmed the 1787 ordinance, and, with slight modifications, renewed it through the Northwest Ordinance of 1789.

Question: Until which year did this territory created by Northwest Ordinance legally exist?
Answer: 1803