Thal is a village and municipality in the Wahlkreis (constituency) of Rorschach in the canton of St. Gallen in Switzerland.

After the First World War, the House of Hohenzollern-Sigmaringen was impoverished and Prince Friedrich von Hohenzollern (1891–1965) was forced to sell the Weinburg estate.

The Steyler Mission Society (Societas Verbi Divini, SVD) was found as the buyer.

The 1983 UCI Road World Championships (cycling) took place in Altenrhein, a village in the municipality.

Of the rest of the land, 35.8% is settled (buildings or roads) and the remainder (7.2%) is non-productive (rivers or lakes).

In the North and East, the municipality borders the old bed of the Rhine river (Alter Rhein) and Austria.

The blazon of the municipal coat of arms is Argent a Grape Azure slipped embowed and leaved Vert.

Stadler Rail has a factory at Altenrhein, which constructs railway rolling stock for Switzerland and other countries.

[8] The Schlosslandschaft Rorschach / Alter Rhein, a number of castles in a region along the Rhine river, is designated as part of the Inventory of Swiss Heritage Sites.

The Schlosslandschaft is shared between Berg, Goldach, Mörschwil, Rheineck, Rorschacherberg, St. Margrethen, Steinach, Thal and Tübach.