Cephalonia or Kefalonia island (Greek: Κεφαλονιά or Κεφαλλονιά), formerly also known as Kefallinia or Kephallenia (Κεφαλληνία), is the largest of the Ionian Islands in western Greece. It is also a separate regional unit of the Ionian Islands region, and the only municipality of the regional unit. It was also a former Latin Catholic bishopric Kefalonia–Zakynthos (Cefalonia–Zante) and short-lived titular see as just Kefalonia
The capital of Cephalonia is Argostoli.
The island is about 781 km2 (300 mi2), with a population density of 55 people per km2 (140/mi2). The town of Argostoli has one-third of the island’s inhabitants. Lixouri is the second major settlement, and the two towns together account for almost two-thirds of the prefecture’s population.
Cephalonia lies in the heart of an earthquake zone, and dozens of minor, unrecorded tremors occur each year. In 1953, a massive earthquake destroyed almost all of the settlements on the island, leaving only Fiskardo in the north untouched.
The island has a rich biodiversity, with a substantial number of endemic and rare species. Some areas have been declared a site in the European Union’s Natura 2000 network.