Cedar Hill is a city in Robertson County, Tennessee, United States. As of the 2020 census, the population was 301. Jo Byrns, who became Sp…Cedar Hill is a city in Robertson County, Tennessee, United States. As of the 2020 census, the population was 301. Jo Byrns, who became Speaker of the House of Representatives, was born in Cedar Hill on July 28, 1869. The local elementary school and high school are named for him.