It lies north-west of Nea Kameni, a small island formed in recent centuries by volcanic activity and thus marking the centre of the island group.

Therasia has a land area of 9.299 square kilometres (3.590 sq mi) and its population was 249 inhabitants at the 2021 census.

It is part of the municipal unit of Oia (Δημοτική Ενότητα Οίας).

At Knossos, in a LMIIIA context (14th century BC), seven Linear B texts while calling upon "all the gods" make sure to grant primacy to an elsewhere-unattested entity called qe-ra-si-ja and, once, qe-ra-si-jo.

[2] Thirasia is also the book of Greek poet Dimitris Varos that became a music album and theatrical performance by Greek composer Giannis Markopoulos under the title Daring Communication - Electric Theseus.