OHIO, a river of North America. It is formed by the junction of the Alleghany and Monongahela rivers, which unite at Pittsburg, and take the name of Ohio. After a course of 1188 miles, it falls into the Mississippi in lat. 37. receiving fifteen rivers in its progress. During the high water of spring and autumn it is navigated by ships of 300 tons, and at all seasons by boats. The rapids at Louisville are the only obstruction; but the navigation will be continued here by a canal.