Tallassee is a city on the Tallapoosa River, located in both Elmore and Tallapoosa counties in the U.S. state of Alabama. At the 2020 censu…Tallassee is a city on the Tallapoosa River, located in both Elmore and Tallapoosa counties in the U.S. state of Alabama. At the 2020 census, the population was 4,763. It is home to a major hydroelectric power plant at Thurlow Dam operated by Alabama Power Company.