Glenn was the last surviving member of the original seven "Right Stuff" Mercury astronauts.
"John Glenn is, and always will be, Ohio's ultimate hometown hero, and his passing today is an occasion for all of us to grieve," Ohio Governor John Kasich said in a statement.
Glenn was credited with reviving U.S. pride after the Soviet Union's early domination of manned space exploration. His three laps around the world in the Friendship 7 capsule on Feb. 20, 1962, forged a powerful link between the former fighter pilot and the Kennedy-era quest to explore outer space as a "New Frontier."