The name of the island (Kefalonia) derives from King Kefalus, who had married the daughter of the King and hero, Theseus. According to the legend, he came to Kefalonia island because he had killed his wife. Kephalus' descendant, according to the historical researchers, is Odysseus, resourceful and ingenious hero of Homer.
It is said that it is the real Ithaca, but the researchers believe that it was the action base of Odysseus and not the Homeric Ithaca. During the ancient times, the island was divided in 4city- states: the state of Sami, Pali, Krani and Pronea. Thucydides, justifiably characterized Kefalonia as "tetrapolin".
The archaeologist N. Kyparissis, referring to the Cyclopean Walls and the walls of the ancient Krani, states that in these walls, one can observe all the stages of the historical development of the island, from the ancient times until the years of the Roman Empire, a period of 3.000 years. The island, according to the archaeological findings, flourished in the Mycenaean period, 1500 BC and communicated with Ithaca, Lefkada and the islands of Cyclades. This communication ended after the explosion of the volcano of Santorini.
During the Hellenistic times, Kefalonia was politically influenced by Corinth and Athens, where the latter used it as a base of their operations against Sparta.

Since 373 BC the island and the Ionian Sea were part of the alliance of Athens.
Around 189 BC the island passed to the Roman Empire. Remarkable is the great resistance of the inhabitants of Sami, which lasted 4 months. Later on, because of their resistance, the inhabitants of Sami were sacked and sold as slaves.
The island, in 394 - 1185, was one of the Ionian issues of the Byzantine Empire, the "Issue of Kefallinia", which helped to prevent the attacks of the Arabian pirates . From 1185 and for some time, the island was free and independent until 1195, when the island passed under the Venetian domination and the authority of Orsini.
In 1357, the island is dominated by Tokkos and in 1479 by Turks. The turkish domination lasted 17 years. The turkish domination resulted in the decline of the island in many areas.

 The capital of the island, due to commercial advantages, was transferred, in 1757, to Argostoli, where it remains until today the largest city, port and touristic resort. The turning over of the island to the Venetians is represented in the painting of the Cretan painter Georgio Klonza, which is kept in the Markiani Library of Venice. Argostoli, the capital of the island, was govened by 17 Venetians, until Jacob Manin handed the island over to the French.
The influence from the west in the island is obvious in the civilization and particularly in the education, since the youngs who were studying in Venice and Pizza used to bring liberal ideas to the island.
It was under the Venetian domination until 1797 and played an important part in the Mediterranean area, since it was the crossing point of the Venetian troops to the Middle East. The ports of Sami, Fiskardou and Atheva were refuge for the Venetian navy.
During the years of French domination, the island organized the education and founded French speaking schools, a National Library and a printing-office. With anti-French uprisings, the island, in 1798, with the leaders Ousakof and Katir Bey, passes to Russian-Turkish domination. The inhabitants of the island, with delegates to Constantinople and Petroupoli, and with direct communication with the representatives of the other Ionian Islands, try to gain their official freedom and independence, something that they finally succeeded. So, in 1800, the treaty of Constantinople, establishes the Ionian Islands as a united state, the first independent greek state known as the "State of the Seven United Islands".
In an intense atmosphere of inner conflicts, the state of the Ionian Islands collapsed in 1807 and passed to the French, for the second time. In 1809, and after the crushing of French powers, the island was seized by the English, with General Oswald in the lead.
Despite the English domination in the island, the inhabitants of Kefalonia, like most of the inhabitants of the Ionian Islands, participated in the Independence War of 1821. Their participation was due to the effects of the French revolution, the western influences and the continuous socio-political changes in the island.

In 1823, in the years of the Greek revolution, Lord Byron was living in the island where he wrote "Don Juan"; he, then, went to fight in the besieged Mesologgi, where he died. Despite Greece's freedom from the Turkish yoke, the island was still in bondage. The historical revolts of 1848 and 1849 marked the history of the island.
Finally, the treaty of London, in 1863, allowed the union of the island with the rest of the Greek state and the destiny of the island is the same as the destiny of the Greek state, from 1864 and after.