After the war ended in early 1865, Cook moved to Americus, Georgia, where he set up a law practice and was active in local and state politics. From 1873 to 1883, Cook was a member of the United States House of Representatives as a Democrat, serving a district comprising part of southwest Georgia. He became Georgia's Secretary of State in 1890, at the specific request of long-serving Secretary of State Nathan Crawford Barnett, made prior to his death in office. Cook was part of the commission that built Georgia's state capitol building in Atlanta.
