The Thurgau (Turgowe, Turgovia) was a pagus of the Duchy of Alamannia in the early medieval period. A County of Thurgau (Landgrafschaft Thurgau) existed from the 13th century until 1798. Parts of Thurgau were acquired by the Old Swiss Confederacy during the early 15th century, and the entire county passed to the Confederacy as a condominium in 1460.
The county became the Canton of Thurgau within the Helvetic Republic in 1798, and with the Act of Mediation of 1803 a canton of the restored Confederacy.