CNN reported the details of Cooper's death had not yet been released.
A native of Oklahoma, Cooper entered the U.S. Marine Corps in 1945 and later became a test pilot. In 1959, Cooper, along with Alan Shepard, Gus Grissom, John Glenn, M. Scott Carpenter, Walter Schirra Jr. and Deke Slayton, was named a Project Mercury astronaut.
"I would have liked to have been one of the crew that landed on the moon, but it just didn't work out that way," Cooper told CNN in 2000, adding in-house politics kept him off the moon flight. "I certainly don't harbor any bitterness or anger."
After retiring from NASA and the U.S. Air Force as a colonel in 1970, he served as a technical consultant to aerospace, electronics and energy firms and as vice president for research and development for Walter E. Disney Enterprises Inc.
After his NASA and military retirement, Cooper accused the U.S. government of covering up its knowledge of extraterrestrial activity.
"For many years I have lived with a secret ... I can now reveal that every day, in the U.S.A., our radar instruments capture objects of form and composition unknown to us," he said.