You can find on the Great Lakes General History page of this site over 40 books and articles about the ‘Old Northwest’ region before the middle of the 19th century. There are works by professional historians as well as by popular writers.
A sample of the titles:
Cox, Isaac J. , “The Indian as a Diplomatic Factor in the History of the Old Northwest” (1909)
McMechen, James H., Legends of the Ohio Valley, or, Thrilling Incidents of Indian Warfare (1887)
Moore, Charles, The Northwest under Three Flags, 1635-1796 (1900)
Roosevelt, Theodore, The Winning of the West (1889-1896)
Turner, Frederick Jackson, “The Place of the Ohio Valley in American History” (1911)