The Northwest Ordinance of 1787 said that the land north of the Ohio River and east of the Mississippi River would eventually become part of the United States . 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 Freedom Ordinance or `` The Ordinance of 1787 '' ) was an act of the Congress of the Confederation of the United States . The primary effect of the ordinance was the creation of the Northwest Territory as the first organized territory of the United States out of the region south of the Great Lakes , north and west of the Ohio River , and east of the Mississippi River .