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.

Lucas County is a county located in the northwestern part of the U.S. state of Ohio. It is bordered to the east by Lake Erie, and to the southeast by the Maumee River, which runs to the lake. As of the 2020 census, the population was 431,279. Its county seat and largest city is Toledo, located at the mouth of the Maumee River on the lake. The county was named for Robert Lucas, 12th governor of Ohio, in 1835 during his second term. Its establishment provoked the Toledo War conflict with the Michigan Territory, which claimed some of its area. Lucas County is the central county of the Toledo Metropolitan Statistical Area.