Tiffin is a city in and the county seat of Seneca County, Ohio, United States. The population was 19,963 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. As of the census of 2000, there were 18,135 people, 7,330 households, and 4,471 families residing in the city. The population density was (2,792.4/mi²) people per square mile (1,078.9/km²). There were 7,862 housing units at an average density of 1,210.6 per square mile (467.7/km²). The racial makeup of the city was 68.8% White, 18.5% African American, 0.17% Native American, 10.2% Asian, 0.02% Pacific Islander, 0.59% from other races, and 1.00% from two or more races. Hispanic or Latino of any race were 2.5% of the population.