"On the fateful Saturday night the Grove was filled to well over capacity, when at 10:10 PM a small fire broke out in the Melody Lounge located in the basement of the Grove’s main ballroom."
"Within twelve minutes, flames and lethal smoke enveloped the entire Grove complex. By 10:45, firefighters had extinguished all flames and were inside the Grove searching for survivors. But in that short period of time, 492 victims were dead or later died in area hospitals."
"The bulk of the victims were taken to Boston City Hospital. Mass. General received the second largest number with Beth Israel, Carney, Faulkner, Mass. Memorial, Peter Bent Brigham, St. Elizabeth’s, St. Margaret’s, Cambridge City and Malden City receiving lesser numbers."
(Post quoted from Rhode Island Fire Disaster Recalls Memories of Cocoanut Grove. Also, the Boston Globe's archives have an excellent article about the event from the 50th anniversary here: The Cocoanut Grove Inferno.)