Thierachern (Highest Alemannic: Tierachere) is a municipality in the administrative district of Thun in the Canton of Bern in Switzerland .

Thierachern is first mentioned in 1250 as Tierachern.

The area around Thierachern was occupied during the Neolithic era, the Bronze Age and the La Tène era. The remains of a Roman era settlement and graves were discovered under the village church. Additional Roman or early medieval stone lined cists were found near Egg. Other graves, of an indeterminate age, have been found in Oberen Hasliholz, by Halterain and by Wahlen.