Tiffin is a city in and the county seat of Seneca County, Ohio, United States. Tiffin is about 55 miles southeast of Toledo. The population was 17,963 at the 2010 census. The National Arbor Day Foundation has designated Tiffin as a Tree City USA.It is the home of Heidelberg University and Tiffin University. At one time it was noted as a glass and porcelain manufacturing center. Tiffin is home to several elementary schools, Tiffin Middle School, Calvert Catholic Schools, and Columbian High School.