1782 Gnadenhütten massacre: Ninety-six Native Americans in Gnadenhutten, Ohio, who had converted to Christianity are killed by Pennsylvania militiamen in retaliation for raids carried out by other Indians.
1796 Surveyors of the Connecticut Land Company name an area in Ohio "Cleveland" after Gen. Moses Cleaveland, the superintendent of the surveying party.
1803 Ohio is admitted as the 17th U.S. state.
1809 Miami University is chartered by the State of Ohio.
1908 The Collinwood School Fire, Collinwood near Cleveland, Ohio, kills 174 people.
1925 USS ''Shenandoah'' (ZR-1), the United States' first American-built rigid airship, was destroyed in a squall line over Noble County, Ohio. Fourteen of her 42-man crew perished, including her commander, Zachary Lansdowne.
1935 Dr. Robert Smith takes his last drink, and Alcoholics Anonymous is founded in Akron, Ohio, United States, by him and Bill Wilson.
1953 Frances Bolton and her son, Oliver from Ohio, become the first mother and son to serve simultaneously in the U.S. Congress.
1967 Trans World Airlines Flight 553, a Douglas DC-9-15, crashes in a field in Concord Township, Ohio following a mid-air collision with a Beechcraft Baron, killing 26.
1969 The Ohio Fireworks Derecho kills 18 Ohioans and destroys over 100 boats on Lake Erie.
1970 Vietnam War: Kent State shootings: the Ohio National Guard, sent to Kent State University after disturbances in the city of Kent the weekend before, open fire killing four students and wounding nine others. The students were protesting the United States' invasion of Cambodia.
1971 Ohio ratifies the 26th Amendment to the U.S. Constitution, lowering the voting age to 18, thereby putting the amendment into effect.
1985 1985 United States-Canadian tornado outbreak: Forty-one tornadoes hit Ohio, Pennsylvania, New York, and Ontario, leaving 76 dead.
1989 Oba Chandler murders an Ohio family on their Florida vacation by drowning them in Tampa Bay.
1990 The Lower Ohio Valley tornado outbreak spawns 66 confirmed tornadoes in Illinois, Indiana, Kentucky, and Ohio, killing 12. Petersburg, Indiana, is the hardest-hit town in the outbreak, with 6 deaths.
1993 450 prisoners rioted at the Southern Ohio Correctional Facility in Lucasville, Ohio, and continued to do so for ten days, citing grievances related to prison conditions, as well as the forced vaccination of Nation of Islam prisoners (for tuberculosis) against their religious beliefs.