Larissos (Greek: Λαρίσσος) is a former municipality in Achaea, West Greece, Greece. Since the 2011 local government reform it is part of the municipality West Achaea, of which it is a municipal unit. Its seat of administration was in the village Lappas, part of the community Metochi. The municipal unit was named after the river Larissos, which flows through it. It is the westernmost municipal unit of Achaea, stretching along the Ionian Sea coast and the border with Elis to the southern part of the Movri hills. It is about 32 km southwest of Patras is 37and 50 km north of Pyrgos.