In the early United States, the “Old Northwest” represented much of what we would now call the Midwest.
Organized as the Northwest Territory in 1787, it was the area bounded by the Appalachian Mountains, the Great Lakes, and the Mississippi and Ohio Rivers.
Britain had acquired it from France in the French and Indian War, then passed it on to the United States.
In time it became the states of Ohio, Indiana, Illinois, Michigan, and Wisconsin, and part of Minnesota.