Four boys and one girl had been hospitalized after the 7:30 a.m. shooting at Chardon High School that sent students fleeing in panic. The suspect, a male youth, was in custody, police said.
"One student has passed away. That's the sad news for all of us today," Chardon Police Chief Tim McKenna said at a news conference.
The student was identified as Daniel Parmentor, 17, who studied computer science at a nearby vocational school and was waiting in the cafeteria for a bus when the gunman opened fire.
"We are shocked by this senseless tragedy," said a statement from Parmentor's family. "Danny was a bright young boy who had a bright future ahead of him. The family is torn by this loss."
He was one of three victims flown to MetroHealth System's trauma center in Cleveland, where another boy was in critical condition and undergoing surgery, said Maggie Lynch, school superintendent in nearby Auburn. The girl and another boy were in stable and serious condition at a suburban hospital.
The Ohio shooting is the worst at a U.S. high school in 11 months, according to the Brady Center to Prevent Gun Violence.
Emergency vehicles rushed to the scene as students streamed from the building. The entire school district, about 35 miles east of Cleveland, was closed for the day.