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

Context paragraphs:
Nathan Dane: Nathan Dane (December 29, 1752 – February 15, 1835) was an American lawyer and statesman who represented Massachusetts in the Continental Congress from 1785 through 1788.  Dane helped formulate the Northwest Ordinance while in Congress, and introduced an amendment to the ordinance prohibiting slavery in the Northwest Territory.

Strader v. Graham: Strader v. Graham, 51 U.S. 82 (1851), was a case in which the Supreme Court of the United States held that the status of three slaves who went from Kentucky to Indiana and Ohio depended on Kentucky law rather than Ohio law.  The original plaintiff was Christopher Graham, whose three slaves had traveled to Cincinnati, Ohio, aboard a steamboat owned by Jacob Strader and James Gorman and piloted by John Armstrong.  The slaves later escaped to Canada.  The U.S. Supreme Court recognized the authority of the Northwest Ordinance of 1789 over its applicable territories in Strader v. Graham, 51 U.S. 82, 96, 97 (1851), but did not extend the Northwest Ordinance to cover respective states which were later admitted to the Union.

ITV Tyne Tees: ITV Tyne Tees, previously known as Tyne Tees, Channel 3 North East and Tyne Tees Television, is the ITV television franchise for North East England and parts of North Yorkshire.  Tyne Tees is owned and operated by ITV plc under the licensee of "ITV Broadcasting Limited".  The analogue signals in the Tyne Tees region were switched off in 2012, making the station, along with ITV London and UTV, one of the last ITV regions to solely broadcast digitally.  Tyne-Tees Television Ltd and Tyne-Tees Television Holdings still legally exist.  Each of these companies is, along with most other regional companies owned by ITV plc, listed at Companies House as a "Dormant company".

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) was an act of the Congress of the Confederation of the United States (the Confederation Congress), passed July 13, 1787.  The ordinance 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.  It was the response to multiple pressures: the westward expansion of American settlers, tense diplomatic relations with Great Britain and Spain, violent confrontations with Native Americans, the weaknesses of the Articles of Confederation, and the empty treasury of the American government.  It was based upon, but more conservative than Thomas Jefferson's proposed ordinance of 1784.  The 1787 law relied on a strong central government, which was assured under the new Constitution that took effect in 1789.  In August 1789, it was replaced by the Northwest Ordinance of 1789, in which the new Congress reaffirmed the Ordinance with slight modifications.

Northwest Territory: The post-American Revolutionary War Territory Northwest of the River Ohio, more commonly known as the Northwest Territory encompassing most of the pre-war territory of the Ohio Country, parts of Illinois Country, and parts of old French Canada below the Great Lakes was an organized incorporated territory of the United States spanning most or large parts of six eventual U.S. States.  It existed legally from July 13, 1787, until March 1, 1803, when the southeastern portion of the territory was admitted to the Union as the state of Ohio, and the remainder was reorganized by additional legislative actions.

List of counties in Indiana: The U.S. state of Indiana has 92 counties.  Each county serves as the local level of government within its borders.  Although Indiana was organized into the United States since the Northwest Ordinance in 1787, its land was not always available for settlement.  Eventually, land was purchased from Native Americans by treaties and Indian removals.  The oldest counties are generally in the south near the Ohio River, whereas newer ones were in the north in territory acquired later.  The oldest and newest counties in Indiana are Knox County, created in 1790, and Newton County, created in 1859.

St. Clair County, Missouri: St. Clair County is a county located in the western portion of the U.S. state of Missouri.  As of the 2010 census, the population was 9,805.  Its county seat is Osceola.  The county was organized in 1841 and named for General Arthur St. Clair, Governor of the Northwest Territory.  St. Clair was also the 9th President of the United States in Congress Assembled.  Under his Presidency, the Northwest Ordinance and United States Constitution were passed.

Public Land Survey System: The Public Land Survey System (PLSS) is the surveying method developed and used in the United States to plat, or divide, real property for sale and settling.  Also known as the Rectangular Survey System, it was created by the Land Ordinance of 1785 to survey land ceded to the United States by the Treaty of Paris in 1783, following the end of the American Revolution.  Beginning with the Seven Ranges, in present-day Ohio, the PLSS has been used as the primary survey method in the United States.  Following the passage of the Northwest Ordinance, in 1787, the Surveyor General of the Northwest Territory platted lands in the Northwest Territory.  The Surveyor General was later merged with the General Land Office, which later became a part of the U.S. Bureau of Land Management (BLM).  Today, the BLM controls the survey, sale, and settling of the new lands, and manages the State Plane Coordinate System.

Wastelands Ordinance: The Cultivation of Wastelands Ordinance, also known as a Wastelands Ordinance, is an ordinance that presumes that, in a given area, there exists the problem referred to as a tragedy of the commons.  This phrase has been most frequently used by nobles hoping to be able to convince the population that it would be better for a local economy if they were allowed to lay claim to a given piece of land (for private use), thereby implying that this would "correct" the situation, making the land thus claimed yield more produce.  From roughly 1982 onward, however, a body of research has been emerging that suggests that the claimed productivity gains were mostly imaginary, and the only effect it had was that it enriched the new land-owners.  This was argued to apply even more to lands under cultivation by so-called 'native populations', and as such this ordinance was invented to allow the colonial power to 'legally' annex the land.

History of slavery in Illinois: Slavery in Illinois existed for more than a century.  Illinois did not become a state until 1818, but earlier regional systems of government had already established slavery.  French settlers introduced African slavery to the Illinois Country in the early eighteenth century.  French inhabitants of Illinois continued the practice of owning slaves throughout the Illinois Country's period of British rule (1763), as well as after its transfer to the new United States in 1783 (See, Illinois County, Virginia).  The Northwest Ordinance (1787) banned slavery in Illinois and the rest of the Northwest Territory.  Nonetheless, slavery remained a contentious issue, through the period when Illinois was part of the Indiana Territory and the Illinois Territory and some slaves remained in bondage even after statehood until their gradual emancipation by the Illinois Supreme Court.

Supporting paragraphs: Northwest Ordinance Northwest Territory
Answer: 1803