Dianne Odell, 61, had been confined to the 7ft-long metal tube since contracting polio when she was three.
Her home near Memphis, Tennessee, suffered a lengthy power failure and relatives were unable to start a back-up generator।
''Dianne had got a lot weaker over the past several months and she just didn't have the strength to keep going.''
Ms Odell was diagnosed with "bulbo-spinal" polio several years before a vaccine was discovered that stopped the spread of the crippling disease affecting children.
Despite being confined inside the iron lung, she managed to get a high school diploma, take courses at a college and write a book.
Iron lungs - or negative pressure ventilators - were first used in the 1920s.
They work by producing pressure on the lungs that causes them to expand and contract so that patients can breathe.
Odell's iron lung, similar to those used during the US polio epidemics that peaked in the 1950s, was a cylindrical chamber with a seal at the neck.
She lay on her back with only her head exposed and made eye contact with visitors through an angled mirror.
Odell, who was cared for by her parents and other family members, operated a television set with a small blow tube and wrote on a voice-activated computer.
Authorities said the electrical failure had been caused by a tree falling on a power line.
