The U.S. Census Bureau's definition consists of 12 states in the north central United States: Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.
so that's the official answer. yes, it includes ohio.
but the real answer is that it's wherever people call carbonated beverages "pop" instead of "soda" or "coke", which means it actually extends eastward to buffalo, ny and definitely still includes ohio.