Judith Platt, president of the ALA's Freedom to Read Foundation, says Krug died late Saturday at Evanston Hospital in suburban Chicago following a battle with stomach cancer. She says Krug had been ill for more than a year.
Krug's age was not immediately available.
She had been head of the ALA's Office for Intellectual Freedom since 1967.
Banned Books Weeks has been observed since 1982 during the last week of September. ALA officials say the event celebrates intellectual freedom.