The Northwest Ordinance was an order of Congress that created the Northwest Territory, the first official territory of the United States. The Northwest Territory included the area that is now Ohio, Indiana, Illinois, Michigan and parts of Minnesota. The territory existed until 1803, when Ohio became a state.
The Northwest Ordinance was the first legislation of its type to be passed by Congress, and it set a precedent for the way westward expansion in the United States would be handled through the 19th century. It established a method for mapping and admitting new states to the union, rather than expanding existing states.