Ohi'o, next to the Missouri the largest affluent of the Mississippi, is formed by the union of the Alleghany and Monongahela at Pittsburgh, Pennsylvania, and flows west-south-west 975 miles, with a breadth of 400 to 1400 yards. In its course it separates the northern states of Ohio, Indiana, and Illinois from the southern states of West Virginia and Kentucky. Towns on its banks are Pittsburgh, Wheeling, Cincinnati, Louisville (where there are rapids of 22 feet in a mile, with a steamboat canal), Evansville, New Albany, Madison, Portsmouth, Covington, and Cairo. The chief affluents are the Tennessee, Cumberland, Wabash, Kentucky, Great Kanawha, Green, Muskingum, and Scioto. It is usually navigable from Pittsburgh; in 1884 it rose 71 feet.
Ohio, the fourth in population of the states of the American Union, lies between Lake Erie and the Ohio River. It stretches from north to south 210 miles, and from east to west 220 miles; area, 39,964 sq. m., equal to that of Ireland and Wales. The country is an extensive, moderately undulating plain; in many places streams have forced a way through bold cliffs of sandstone. A low ridge enters the state near the north-east corner and crosses it in a south-westerly direction; this 'divide' (1300 feet above sea-level) separates the waters of Lake Erie and the Ohio River. North of this ridge the surface of the country gently declines toward the lake. The central part of Ohio is almost a level plain, about 1000 feet above the sea, slightly inclining southward. The southern part is somewhat hilly, the valleys growing deeper as they approach the Ohio River, whose tributaries here water many extensive and fertile valleys. The coalfields cover over 12,000 sq. m.; and immense deposits of limestone, freestone, and mill-stones abound. In no other state have been found so many evidences of man's antiquity exemplified in implements of stone, bone, copper, and clay; while the most extensive and elaborate systems of earthworks in America are at Newark, near Chillicothe, and on the Miami bluffs near Waynes-ville. Ohio is one of the chief manufacturing states in the Union, leading all others in the manufacture of farm machinery, carriages and wagons, woollen and cotton goods, furniture, and wine and spirits. It has also great rolling-mills and iron-factories, glass-factories, potteries, and oil-works. In agriculture the state is first in the Union in many regards; its annual production of maize is some 155,000,000 bushels, of wheat 40,000,000, of wool about 15,000,000 lb. Cattle and hogs are reared in large numbers. In the southern sections cattle may be left in the fields all winter. The belt adjoining Lake Erie is famous for its fruit; excellent melons are grown in almost all parts of the state. The oilfields and stores of natural gas are sources of wealth.
Ohio is part of the original North-west Territory, claimed mostly by Virginia under charters from English kings. In 1787 the Ohio Company of Associates was organised by soldiers of the revolution war, and under their auspices a large tract of land was purchased from government. In 1788 Marietta and Cincinnati were founded. In 1791 the Indians became troublesome, and in 1794 a signal victory was gained over them by General Wayne. Soon after settlers occupied rapidly the land, and Chillicothe was made the seat of government. In 1803 Ohio was admitted into the Union. Ohio has given birth to four presidents - Grant, Hayes, Garfield, and Benjamin Harrison. The largest cities are Cincinnati, Cleveland, Columbus (the capital), Toledo, Dayton, Youngstown, and Springfield. Pop. (1816)230,760; (1850) 1,980,329; (1870) 2,665,260; (1880) 3,198,062; (1900) 4,157,545.