Shriver, 88, was in critical condition at Cape Cod Hospital in Barnstable since Saturday after she suffered a series of strokes.
Family members were called to Shriver's bedside over the weekend, including son-in-law, California Gov. Arnold Schwarzenegger, who is married to her daughter, Maria Shriver.
Shriver was the fifth of the nine Kennedy children. She founded Special Olympics and her work was inspired, in part, by the struggles of her mentally disabled sister, Rosemary.