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 . It is about 32 km southwest of Patras is 37and 50 km north of Pyrgos.The area is mostly flat, except the Movri hills in the southeast and the lower Mavra Vouna hills in the northwest, near Cape Araxos. Araxos Airport (GPA). The archaeological site of the ancient town of Dyme is located 1 km south.