Glenn, who served four terms as a U.S. senator from Ohio and ran for president in 1984, was born on July 18, 1921, in Cambridge, Ohio.
Glenn, who is recovering from knee surgery, made light of reaching the milestone of his 90th birthday, The Columbus Dispatch reported.
"Well, you know what they say: If I'd known I was going to live this long, I would have taken better care of myself," he said recently.
Glenn entered the history books on Feb. 20, 1962, when an Atlas rocket launched his capsule 160 miles into orbit.
"You didn't really have time to think about it," he said of the acknowledged risks. "Long before you actually got to the flight itself, you sort of made peace with mortality."
Glenn, with his wife, Annie, now calls Columbus home.