Sylvania is a city in Lucas County, Ohio, United States. The population was 19,011 at the 2020 census. Sylvania is a suburb of Toledo, and …Sylvania is a city in Lucas County, Ohio, United States. The population was 19,011 at the 2020 census. Sylvania is a suburb of Toledo, and encompassed by Sylvania Township. Its northern border is the southern border of the state of Michigan.