Since the local government reform in 2011, it a unit within the municipality West Achaea.

[3] 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.

The municipal unit Larissos is subdivided into the following communities (constituent villages in brackets):