Froehlich died Sunday, two weeks after having a stroke, her son, Illinois State Rep. Paul Froehlich, D-Schaumburg, told The New York Times.
Froehlich, who was born Jan. 5, 1915, in New York, contributed time to the Young Christian Workers, a Roman Catholic lay group, and is recognized by many as a pioneer for motherhood, the Times said.
La Leche League formed in 1956 in Franklin Park, Ill., as a platform for women to seek education and support about breastfeeding.
Froehlich became increasingly involved in the league as it grew to La Leche League International in 1964.
She helped author "The Womanly Art of Breast-feeding," a manifesto published as a book in 1963. At least 2 million copies of the book have been printed, the newspaper said.