The Ohio River is a 981-mile-long (1,579 km) river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing in a southwesterly direction from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illinois. It is the third largest river by discharge volume in the United States and the largest tributary by volume of the north-south flowing Mississippi River, which divides the eastern from western United States. It is also the 6th oldest river on the North American continent. The river flows through or along the border of six states, and its drainage basin includes parts of 14 states. Through its largest tributary, the Tennessee River, the basin includes several states of the southeastern U.S. It is the source of drinking water for five million people.

The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four census regions of the United States Census Bureau. It occupies the northern central part of the United States. It was officially named the North Central Region by the U.S. Census Bureau until 1984. It is between the Northeastern United States and the Western United States, with Canada to the north and the Southern United States to the south.