The man, 45-year-old James A. Young, reportedly climbed over a fence to search for his cellphone when the roller coaster "The Raptor" struck the back of his head, according to The Blaze.
An eyewitness reported in WEWS-TV that she saw paramedics trying to revive the school teacher from East Canton.
The amusement park, Cedar Point, shut down a few roller coasters after the incident and expressed its condolencences for the family.
Cedar Point said in a statement: "At 5 p.m. guest entered a restricted, fenced area of Raptor and was struck by the ride." It says its "thoughts and prayers go out to the family."