Elaine Costanzo Duke (born 1958) is an American civil servant. On January 30, 2017, she was nominated by President Donald Trump to become the United States Deputy Secretary of Homeland Security under John F. Kelly. She became acting United States Secretary of Homeland Security on July 31, 2017 when John F. Kelly assumed the office of White House Chief of Staff.
On February 23, 2018, she announced plans to retire from her position as Deputy Secretary in April of the same year, after serving in the federal government of the U.S. for over thirty years.