The history of Ohio includes many thousands of years of human activity. What is now Ohio was probably first settled by Paleo-Indian peoples, who lived in the area as early as 13,000 B.C. A fossil dated between 11,727 and 11,424 B.C. indicates they hunted large game including Jefferson's ground sloth using stone tools. Later ancestors of Native Americans were known as the Archaic peoples. Sophisticated successive cultures of precolonial peoples indigenous peoples, such as the Adena, Hopewell and Mississippian, built monumental earthworks as part of their religious and political expression: mounds and walled enclosures, some of which have survived to the present.

While by the mid-18th century, Europeans engaged historic Native American tribes in present-day Ohio in the fur trade, European-American settlement in the Ohio territory did not expand until after the American Revolutionary War. The United States Congress prohibited slavery in the Ohio Territory. Ohio's population increased rapidly, chiefly by migrants from the Northern Tier of New England and New York. Southerners settled along the southern part of the territory, as they traveled mostly by the Ohio River. After Ohio became a state, citizens still prohibited slavery and some supported the Underground Railroad, as well as establishing colleges that admitted blacks and women. Its citizens' support of public education and political action also reflected New England/Northern Tier values. The state supported the Union in the American Civil War, and more of its people volunteered as soldiers per capita than any other state.

Ohio (ⁱ/oʊˈhaɪ.oʊ/) is a state in the Midwestern United States. Ohio is the 34th most extensive, the 7th most populous, and the 10th most densely populated of the 50 United States. The state's capital and largest city is Columbus.

The name "Ohio" originated from Iroquois word ohi-yo’, meaning "great river". The state, originally partitioned from the Northwest Territory, was admitted to the Union as the 17th state (and the first under the Northwest Ordinance) on March 1, 1803. Although there are conflicting narratives regarding the origin of the nickname, Ohio is historically known as the "Buckeye State" (relating to the Ohio buckeye tree) and Ohioans are also known as "Buckeyes".

The government of Ohio is composed of the executive branch, led by the Governor; the legislative branch, which comprises the Ohio General Assembly; and the judicial branch, which is led by the Supreme Court. Currently, Ohio occupies 18 seats in the United States House of Representatives. Ohio is known for its status as both a swing state and a bellwether in national elections.