Archeological evidence suggests that the Ohio Valley was inhabited by nomadic people as early as 13,000 BC. These early nomads disappeared from Ohio by 1,000 BC, "but their material culture provided a base for those who followed them". Between 1,000 and 800 BC, the sedentary Adena culture emerged. As Ohio historian George W. Knepper notes, this sophisticated culture was "so named because evidences of their culture were excavated in 1902 on the grounds of Adena, Thomas Worthington's estate located near Chillicothe". The Adena were able to establish "semi-permanent" villages because they domesticated plants, which included squash, sunflowers, and perhaps corn. Cultivation of these in addition to hunting and gathering supported more settled, complex villages. The most spectacular remnant of the Adena culture is the Great Serpent Mound, located in Adams County, Ohio.
Around 100 BC, the Adena were joined in Ohio Country by the Hopewell people, who were named for the farm owned by Captain M. C. Hopewell, where evidence of their unique culture was discovered. Like the Adena, the Hopewell people participated in a mound-building culture. Their complex, large and technologically sophisticated earthworks can be found in modern-day Marietta, Newark, and Circleville. The Hopewell, however, disappeared from the Ohio Valley in about 600 AD. Little is known about the people who replaced them. Researchers have identified two additional, distinct prehistoric cultures: the Fort Ancient people and the Whittlesey Focus people. Both cultures apparently disappeared in the 17th century, perhaps decimated by infectious diseases spread in epidemics from early European contact. The Native Americans had no immunity to common European diseases. Some scholars believe that the Fort Ancient people "were ancestors of the historic Shawnee people, or that, at the very least, the historic Shawnees absorbed remnants of these older peoples."
American Indians in the Ohio Valley were greatly affected by the aggressive tactics of the Iroquois Confederation, based in central and western New York. After the so-called Beaver Wars in the mid-17th century, the Iroquois claimed much of the Ohio country as hunting and, more importantly, beaver-trapping ground. After the devastation of epidemics and war in the mid-17th century, which largely emptied the Ohio country of indigenous people by the mid-to-late 17th century, the land gradually became repopulated by the mostly Algonquian-speaking descendants of its ancient inhabitants, that is, descendants of the Adena, Hopewell, and Mississippian cultures. Many of these Ohio-country nations were multi-ethnic (sometimes multi-linguistic) societies born out of the earlier devastation brought about by disease, war, and subsequent social instability. They subsisted on agriculture (corn, sunflowers, beans, etc.) supplemented by seasonal hunts. By the 18th century, they were part of a larger global economy brought about by European entry into the fur trade.
The indigenous nations to inhabit Ohio in the historical period included the Miamis (a large confederation); Wyandots (made up of refugees, especially from the fractured Huron confederacy); Delawares (pushed west from their historic homeland in New Jersey); Shawnees (also pushed west, although they may have been descended from the Fort Ancient people of Ohio); Ottawas (more commonly associated with the upper Great Lakes region); Mingos (like the Wyandot, a group recently formed of refugees from Iroquois); and Eries (gradually absorbed into the new, multi-ethnic "republics," namely the Wyandot). Ohio country was also the site of Indian massacres, such as the Yellow Creek Massacre, Gnadenhutten and Pontiac's Rebellion school massacre.
During the 18th century, the French set up a system of trading posts to control the fur trade in the region. In 1754, France and Great Britain fought a war that was known in North America as the French and Indian War and in Europe as the Seven Years War. As a result of the Treaty of Paris, the French ceded control of Ohio and the remainder of the Old Northwest to Great Britain.
Pontiac's Rebellion in the 1760s, however, posed a challenge to British military control. This came to an end with the colonists' victory in the American Revolution. In the Treaty of Paris in 1783, Britain ceded all claims to Ohio country to the United States.
The United States created the Northwest Territory under the Northwest Ordinance of 1787. Slavery was not permitted in the new territory. Settlement began with the founding of Marietta by the Ohio Company of Associates, which had been formed by a group of American Revolutionary War veterans. Following the Ohio Company, the Miami Company (also referred to as the "Symmes Purchase") claimed the southwestern section, and the Connecticut Land Company surveyed and settled the Connecticut Western Reserve in present-day Northeast Ohio.
The old Northwest Territory originally included areas previously known as Ohio Country and Illinois Country. As Ohio prepared for statehood, the Indiana Territory was created, reducing the Northwest Territory to approximately the size of present-day Ohio plus the eastern half of the Lower Peninsula of Michigan and the eastern tip of the Upper Peninsula.
Under the Northwest Ordinance, areas of the territory could be defined and admitted as states once their population reached 60,000. Although Ohio's population numbered only 45,000 in December 1801, Congress determined that the population was growing rapidly and Ohio could begin the path to statehood. The assumption was that it would exceed 60,000 residents by the time it was admitted as a state.
On February 19, 1803, President Jefferson signed an act of Congress that approved Ohio's boundaries and constitution. However, Congress had never passed a resolution formally admitting Ohio as the 17th state. The current custom of Congress declaring an official date of statehood did not begin until 1812, with Louisiana's admission as the 18th state. Although no formal resolution of admission was required, when the oversight was discovered in 1953, Ohio congressman George H. Bender introduced a bill in Congress to admit Ohio to the Union retroactive to March 1, 1803. At a special session at the old state capital in Chillicothe, the Ohio state legislature approved a new petition for statehood that was delivered to Washington, D.C. on horseback. On August 7, 1953 (the year of Ohio's 150th anniversary), President Eisenhower signed an act that officially declared March 1, 1803 the date of Ohio's admittance into the Union.
Although many Native Americans had migrated west to evade American encroachment, others remained settled in the state, sometimes assimilating in part. In 1830 under President Andrew Jackson, the US government forced Indian Removal of most tribes to the Indian Territory west of the Mississippi River.
In 1835, Ohio fought with Michigan in the Toledo War, a mostly bloodless boundary war over the Toledo Strip. Congress intervened, making Michigan's admittance as a state conditional on ending the conflict. In exchange for giving up its claim to the Toledo Strip, Michigan was given the western two-thirds of the Upper Peninsula, in addition to the eastern third that was already considered part of the state.
Ohio's central position and its population gave it an important place during the Civil War. The Ohio River was a vital artery for troop and supply movements, as were Ohio's railroads. Ohio contributed more soldiers per-capita than any other state in the Union. In 1862, the state's morale was badly shaken in the aftermath of the battle of Shiloh, a costly victory in which Ohio forces suffered 2,000 casualties. Later that year, when Confederate troops under the leadership of Stonewall Jackson threatened Washington, D.C., Ohio governor David Tod still could recruit 5,000 volunteers to provide three months of service. Ohio historian Andrew R. L. Cayton writes that almost 35,000 Ohioans died in the conflict, "and some thirty thousand carried battle scars with them for the rest of their lives." By the end of the Civil War, the Union's top three generals–Ulysses S. Grant, William Tecumseh Sherman, and Philip Sheridan–were all from Ohio.
In 1912 a Constitutional Convention was held with Charles B. Galbreath as secretary. The result reflected the concerns of the Progressive Era. It introduced the initiative and the referendum. In addition, it allowed the General Assembly to put questions on the ballot for the people to ratify laws and constitutional amendments originating in the Legislature. Under the Jeffersonian principle that laws should be reviewed once a generation, the constitution provided for a recurring question to appear on Ohio's general election ballots every 20 years. The question asks whether a new convention is required. Although the question has appeared in 1932, 1952, 1972, and 1992, it has never been approved. Instead constitutional amendments have been proposed by petition to the legislature hundreds of times and adopted in a majority of cases.
Eight U.S. presidents hailed from Ohio at the time of their elections, giving rise to its nickname "Mother of Presidents", a sobriquet it shares with Virginia. It is also termed "Modern Mother of Presidents," in contrast to Virginia's status as the origin of presidents earlier in American history. Seven presidents were born in Ohio, making it second to Virginia's eight. Virginia-born William Henry Harrison lived most of his life in Ohio and is also buried there. Harrison conducted his political career while living on the family compound, founded by his father-in-law, John Cleves Symmes, in North Bend, Ohio. The seven presidents born in Ohio were Ulysses S. Grant, Rutherford B. Hayes, James A. Garfield, Benjamin Harrison (grandson of William Henry Harrison), William McKinley, William Howard Taft and Warren G. Harding.