The Washington Post on Monday first reported Calley's death, which happened in April, according to a death certificate the newspaper cited. The New York Times, citing Social Security Administration death records, also reported Calley's death.
Neither paper reported a cause of death. Calls to numbers listed for Calley's son, William L. Calley III, were not returned.
American soldiers killed 504 people on March 16, 1968, in Son My, a collection of hamlets between the central Vietnamese coast and a ridge of misty mountains, in an incident known in the West as the My Lai Massacre. The killings shocked the U.S. and galvanized the anti-war movement.
Initially charged in an Army court martial for 102 deaths, Calley was sentenced to life in prison in 1971 for the killing of 22 civilians. He was behind bars only three days before then President Richard Nixon ordered him released under house arrest. After being discharged from the service, he lived out his life quietly in Georgia.