Ohio ( oh-HY-oh) is a state in the Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the west, and Michigan to the northwest. Of the 50 U.S. states, it is the 34th-largest by area. With a population of nearly 11.8 million, Ohio is the seventh-most populous and tenth-most densely populated state. Its capital and most populous city is Columbus, with other large population centers including Cleveland, Cincinnati, Dayton, Akron, and Toledo. Ohio is nicknamed the "Buckeye State" after its Ohio buckeye trees, and Ohioans are also known as "Buckeyes".

Ohio derives its name from the Ohio River that forms its southern border, which, in turn, originated from the Seneca word ohiːyo', meaning "good river", "great river", or "large creek". The state was home to several ancient indigenous civilizations, with humans present as early as 10,000 BCE. It arose from the lands west of the Appalachian Mountains that were contested by various native tribes and European colonists from the 17th century through the Northwest Indian Wars of the late 18th century. Ohio was partitioned from the Northwest Territory, the first frontier of the new United States, becoming the 17th state admitted to the Union on March 1, 1803, and the first under the Northwest Ordinance. It was the first post-colonial free state admitted to the union and became one of the earliest and most influential industrial powerhouses during the 20th century.

Although it has transitioned to a more information- and service-based economy in the 21st century, it remains an industrial state, ranking seventh in GDP as of 2019, with the third-largest manufacturing sector and second-largest automobile production. Modeled on its federal counterpart, Ohio's government is composed of the executive branch, led by the governor; the legislative branch, consisting of the bicameral Ohio General Assembly; and the judicial branch, led by the state Supreme Court. Ohio occupies 15 seats in the United States House of Representatives, the seventh-largest delegation. Seven presidents of the United States have come from Ohio, earning it the moniker "the Mother of Presidents".