Larissos is a former municipality in Achaea, West Greece, Greece. Since the local government reform in 2011, it a unit within the municipality West Achaea. The municipal unit has an area of 225.729 km2. 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 and 50 km north of Pyrgos.