Toggenburg is a region of Switzerland. It corresponds to the upper valley of the river Thur and that of its main tributary, the Necker. Since 1 January 2003, Toggenburg has been a constituency (Wahlkreis) of the canton of St. Gallen (SFOS number 1727).
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 () and on the southwest by that of the Churfirsten () and of the Speer (). It is a fertile valley of about in length from the source of the river to Wil.
At Wildhaus, the highest village (), the house wherein Huldrych Zwingli, the Swiss Reformer, was born in 1484, is still shown. Other villages are Lichtensteig, Kirchberg and Wattwil.
There are traces of the paleolithic Mousterian Industry throughout the Appenzell Alps, in the Toggenburg notably in Wildenmannlisloch cave.
The upper Thur valley was part of the province of Raetia in the Roman era, and was reached by Alemannic-speaking settlers only in the early medieval period. This is evidenced by a substantial substrate of Romance toponyms in the upper Toggenburg (upstream of Stein).
The name of the region is derived from that of the House of Toggenburg (named for their castle near Kirchberg) who ruled over parts of the Toggenburg region since the 12th century, in the 13th century taking the title of counts (comes) and extending their domain to include all of the upper Thur valley.
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 to the abbot of St. Gall in 1468.
Part of the Toggenburg followed the Swiss Reformation led by Zwingli, and the valley declared itself independent in 1530, but was forced to re-submit to the Abbot of St. Gall in 1538.