According to mythology, the first inhabitants of the island were the Nymphs who lived near the springs, because of which Kea was then called Hydrousa. After they were driven out by a lion, a drought hit the island until the arrival of the son of Apollo Aristaeus, at the request of the inhabitants. He saved the island from drought and drought by sacrificing to Zeus Icmaeus and ensuring that cool winds blew on the island during the hot summer months.
The name Keos is due to the first named settler of the island, Keos, leader of the Lokras, from Nafpaktos. The bay of Agios Nikolaos and more specifically the peninsula of Ag. Irini, is the center of the prehistoric settlement of the island. During the Neolithic period, Cape Kefala was home to one of the earliest settlements in the Cyclades, while during the Bronze Age the organized and fortified settlement of Agia Irini was a naval and cultural station between mainland Greece and the Cycladic-influenced Aegean. culture (3rd millennium BC) and the Creto-Mycenaean world (2nd millennium BC).
In historical times the island was inhabited by the Ionians. During the Archaic years (7th-6th centuries BC) the Tetrapolis of Keos was founded, which consisted of Ioulida, Korissia, Poiiessa and Karthaia, the locations of which could be determined from the geomorphology and from inscriptions testimonials. The city-states of Kea highlight it culturally and economically, while at the same time the archaic sanctuaries of Korissia and Agia Irini are also developing. The lyric poets Simonides Keios and Bacchylides, the sophist Prodikos, the physician Erasistratus and the philosopher Aristotle are some of the influential figures of Antiquity who were born and worked not only in Kea, but also in other centers of the Aegean.
In the Persian wars, Keos took part with its own ships in the naval battle of Artemisium and Salamis, while its proximity to Athens turned it into a trade center and contributed to its economic prosperity with the exploitation of iron and milt mines and its inclusion in Athenian Alliance.
During the Peloponnesian War the Keians fought on the side of the Athenians, while they also took part in the Sicilian campaign. In 377/376 BC the cities of Kea joined the Second Athenian Alliance and in 338 BC they fought against the Macedonians, in the battle of Chaeronea. In Hellenistic times, the island was part of the Commons of the Islanders and the subject of a dispute between the Successors, which led to the end of the autonomy of the four cities.
During the Roman period, Antony ceded Kea to Athens until 212 AD, when with the decree of Caracalla it came under Roman rule.
During the Byzantine period, from the 9th c. Kea belonged to the Theme of the Aegean, while pirate raids forced the inhabitants to fortify themselves inside the island. In 1207 it succumbed to the Franks and was included in the Duchy of the Aegean under Marko Sanudo until 1537, when it fell into the hands of the Ottomans and was colonized by Arvanite populations. Possibly then the name Tzia also prevails. Her official Ottoman name, however, was Murtat.
Kea suffered great damage in 1668 during the Venetian-Ottoman war, due to its support for the Venetians. From the same time we have information about the existence of a community mechanism on the island, which bore the official title "Community of the Island of Zia".
Kea flourished in the 18th century. It is the time when it becomes a commercial and transit center of the region and maintains commercial relations with consulates of all the Great Powers. Its population is estimated to have been 3,000-5,000 inhabitants. It enjoyed relative administrative autonomy. During the Russo-Ottoman War (1787-1792) the envoy officer of Tsarist Russia Lambros Katsonis used the port of Tzia as a base of operations, while in 1789 he was besieged there by the Ottomans and escaped through a narrow strip of land (the Katsoni Strait) . Kea participated in many battles of the Revolution of 1821 (Acropolis, Tripoli, Peta).
After liberation from the Turkish yoke and the establishment of the neo-Greek state, the island developed strong institutions of self-government and turned into a thriving agricultural, livestock and commercial community. Immigration abroad as well as internal immigration during the 20th century dramatically reduced the population on the island, which gradually began to decline. From 1941 it experienced the occupation of the Axis powers. It was liberated in 1944, after the withdrawal of the German troops.