Althofen (Slovene: Stari Dvor) is a town in the district of Sankt Veit an der Glan in the Austrian state of Carinthia.

The present-day parish church with its massive steeple is the only one in Carinthia dedicated to Saint Thomas of Canterbury, it was built about 1400, with Baroque ornamentation in the 18th century and Neo-Gothic embellishment in 1908–10.

In 1230 Althofen received market rights as an important trading venue, mainly for iron (Noric steel) from the nearby mines of Hüttenberg.

In 1897 the local ironworks were purchased by Baron Carl Auer von Welsbach (1858–1929), the inventor of ferrocerium (Auermetall).

He developed the iron mill to a chemical plant, the later Treibacher Industrie AG, the main employer in Althofen up to today.