Pausanias, in his work Description of Greece, refers to Myonia as a town farther inland from Amfissa and above it, thirty stades away.
During the Ottoman occupation of Greece, Agia Efthymia held a leading role in the region of Parnassida and had one of the only three schools in Phocis, established by the teacher and monk Nikodimos Kavassilas, who was born in Agia Efthymia in 1595.