Toggenburg is the name given to the upper valley of the Thur River, in the Swiss Canton of St. Gallen. Currently, it is one of the eight constituencies into which the canton is divided.

The valley descends in a northwestern direction from the watershed between the Rhine and the Thur, and is enclosed on the northeast by the chain of the Säntis (8216 ft) and on the southwest by that of the Churfirsten (7566 ft) and of the Speer (6411 ft). It is a fertile valley of about 45 kilometres in length from the source of the river to Wil on the railway line between Winterthur and St. Gallen. The upper half is traversed by an excellent road, while from Nesslau there is a railway to Wil (155 m).

At Wildhaus, the highest village (3632 ft), the house wherein Huldrych Zwingli, the Swiss Reformer, was born in 1484, is still shown. Other villages are Lichtensteig, Kirchberg and Wattwil.

The extinction of the main line of the counts of Toggenburg (1436) led to the Old Zürich War (1440–46) ultimately resulting in the temporary expulsion of Zürich from the Swiss confederacy. Eventually, the Toggenburg passed to the lord of Raron (in Valais), who sold it in 1468 to the abbot of St. Gall.