The dinner, attended by 835 people, was hosted in Antioch in California on Thursday.
Eight patients were treated on Friday and Saturday, according to representatives from Sutter Delta Medical Center.
Three died, five were released, and one remained in the hospital as of yesterday.
The cause of the deaths and illness is still under investigation, though authorities suspect it to a suspected case of food poisoning, Contra Costa Health Services spokeswoman Victoria Balladares said.
Balladares said she did not know what organisation was responsible for preparing the meals, but said it was a non- profit group serving a traditional Thanksgiving meal to roughly 835 people.