Stjorn is probably one of the eldest names that have been applied in the Fosen peninsula north of Trondheim. The name is connected to the geological fault stretching from Smøla/Hitra in the west almost to the border to Sweden in the east. The fault is dated back to about 350 million years ago when the terrain broke up and the northern part of it lifted up on top of the southern part, leaving a south-bound rocky wall as an almost straight line in the landscape hundreds of kilometers. Today the fault is below sea level in the west, forming the northern side of the Stjorn fjord, it comes up to surface in the Råkvåg area where it forms the northern part of the Stjorn river system, and continues as a hundred meters steep mountain wall further to the east.
The name was known already in the time of the vikings when the fjord Stjorn was the sea access to the capital Nidaros (today Trondheim). During the Dane rule the writing was changed to both Skiørn and Stjørn, but the pronunciation was all the time as in the old Norse language. The name Stjorn got official between 1899 and 1964, when ‘Stjorn’ (Stjørna) became one of the Norwegian municipalities. Stjørna has the same name base as today’s airport municipality for Trondheim, Stjørdal. Both names are explained with a reference to ‘steering’. The Stjorn fjord is a steering fjord at sea, the same way as Stjørdal is a steering valley.