Thurgau, canton, northeastern Switzerland. It is bordered on the north by Lake Constance (Bodensee), by the Rhine River on the northwest, and by the cantons of Sankt Gallen on the south and Zürich and Schaffhausen on the west. With an area of 383 square miles (991 square km), it is divided into three hill masses: one stretching along the lake; another inland, bounded north by the Thur River and south by its affluent, the Murg; and the third at the southern extremity of the canton, merging into the pre-Alpine zone of Mount Hörnli. Frauenfeld (q.v.) is the capital.
Inhabited by lake dwellers (the Pfyn culture) in prehistoric times, it was later part of the Roman province of Raetia for several centuries until ad 450, after which it passed to the Alamanni, a Germanic tribe. From the 8th century on, it appeared as a political unit, extending as far west as the Reuss River and as far south as the foot of the Alps. In the later European Middle Ages the county of Thurgau, already much reduced in size, belonged successively to the dukes of Zähringen and the counts of Kyburg. With the extinction of the Kyburg line in 1264, the county passed to the Habsburgs, from whom it was seized by the confederated Swiss states in 1460 and thenceforth ruled as a subject district. In 1798 it became a canton of the Helvetic Republic and in 1803 a full member of the Swiss Confederation. Its cantonal constitution dates from 1869.
Thurgau is a prosperous agricultural area known for apples and pears and for cider making. There are vineyards along the lake and in the Thur valley. Industries include the manufacture of metal products, machinery, and beverages, as well as food processing.. The canton is traversed by two railways with several branch lines. The population is mostly German speaking and more than two-fifths Protestant and about one-third Roman Catholic. Pop. (2007 est.) 235,764.