Ohio is a midwestern state of the United States. Part of the Great Lakes region, Ohio has long been a cultural and geographical crossroads. At the time of European contact and in the years which followed, Native Americans in today's Ohio included the Iroquois, Miamis, and Wyandots. Beginning in the 1700s, the area was settled by people from New England, the Middle States, Appalachia, and the upper south.

Prior to 1984, the United States Census Bureau considered Ohio part of the North Central Region. That region was renamed "Midwest" and split into two divisions. Ohio is now in the East North Central States division.

The name "Ohio" derives from the Seneca word ohi:yo’, meaning "beautiful river" or "large creek", which was originally the name of both the Ohio River and Allegheny River.

Ohio was the first state admitted to the Union under the Northwest Ordinance. Its U.S. postal abbreviation is OH; its old-style abbreviation is O.