Cleveland.com reported that Glenn, 95, had heart valve replacement surgery in 2014.
The reasoning for this hospitalization is not clear. Glenn's executive assistant, Kathy Dancey, said she had no further information.
"Anybody who's 95, any illness is always bad," said college spokesman Hank Wilson. He said Glenn is at the James Cancer Hospital at Ohio State, but it does not necessarily mean he has cancer.
According to Cleveland.com, Glenn's health has declined in the last few years. The Associated Press reported that when Glenn spoke at the renaming ceremony for Columbus, Ohio's airport, he said some of his eyesight had been lost because of macular degeneration and a small stroke.
John Glenn was born July 18, 1921 in Cambridge, Ohio.
He enlisted in the Navy as an aviation cadet in March 1942 following the Dec. 7, 1941 attack on Pearl Harbor.
On April 6, 1943, he married the former Anna Margaret Castor, his childhood playmate and high school sweetheart. They went on to have two children, Carolyn Ann Glenn and John David Glenn, and have two grandchildren.
Before making history in space, Glenn set the transcontinental speed record from Los Angeles to New York in July 1957: Three hours and 23 minutes.
Glenn received orders for combat duty in Korean War in 1953, flying 63 missions with Marines and 27 missions as an exchange pilot with the U.S. Air Force.
He became a Marine test pilot in 1954. In 1965, Glenn retired from the Marine Corps as a colonel.
Glenn made history as the first American to orbit the earth in 1962, piloting the Mercury-Atlas 6 "Friendship 7" spacecraft and completing three orbits during the five-hour flight.
Initially running for the U.S. Senate in 1964, he was forced to bow out of the running in the primaries when he sustained a head injury in an accident. Once he recovered from the accident, he became a vice president then president at Royal Crown Cola.
He became a Democratic senator representing Ohio in 1974 and served until 1993, completing four terms. He became the oldest man to fly in space when he served as a payload specialist on the Space Shuttle Discovery in 1998. That 9-day mission was accomplished in 134 Earth orbits.
Laura A. Bischoff with Dayton Daily News contributed to this story.
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