Cephalonia is the regional unit’s major island, covering 773 km2 (300 mi2) and having a population density of 55 persons per km2 (140/mi2). Argostoli is home to one-third of the island’s population. Lixouri is the prefecture’s second largest town, and the two towns combined account for about two-thirds of the prefecture’s population.
Petalas Island and Asteris Island are the two big islands, however they are deserted.
Cephalonia is located in an earthquake zone, and each year, hundreds of tiny, unrecorded tremors occur. A large earthquake devastated virtually all of the island’s villages in 1953, leaving only Fiskardo in the north unscathed.
Melissani Lake, the Drogarati caverns, and the Koutavos Lagoon near Argostoli are also noteworthy natural features.
The island boasts a diverse biodiversity, including several indigenous and uncommon species. Some locations have been designated as Natura 2000 sites by the European Union.
Mount Ainos, with a height of 1628 meters, is the highest point on the island; to the west-northwest are the Paliki mountains, which include Lixouri, as well as Geraneia (Gerania) and Agia Dynati. The summit of Mount Ainos is a natural park with fir trees.
Forestry is uncommon on the island, although its wood production is among the greatest in the Ionian islands, but less than that of Elia in the Peloponnese. Forest fires were prevalent in the 1990s and early 2000s, and they continue to represent a significant hazard to the people.
Cephalonia is well-known for its endangered loggerhead turtle population, which nests on several beaches around the island’s south coast. A tiny colony of the endangered Mediterranean monk seal, Monachus monachus, lives along the island’s shore as well, particularly on areas of the coast that are inaccessible to people owing to the topography. Caves along this stretch of coast are great places for seals to give birth to their pups and nurse them for the first few months of their life.
The island is known to be home to the European pine marten.
Over 200 bird species have been sighted on the island.