Kea has been inhabited since the late Neolithic times. At that time, the island was known as Hydroussa. However, the history of Kea is intertwined with mythology. According to the myths, the vast springs and fountains of this island were home to nymphs. The nymphs are said to be chased off Kea by a fierce lion sent by the gods, who were jealous of the island's beauty. To please the animal, the inhabitants carved a lion statue on the rocks, which still exists outside of Ioulida.
According to the gods' plans, the place became dry and started being ruled by the star Sirius. After that, the displeased inhabitants asked for help from the son of Apollo, the semi-god Aristaios, and the nymph Kyrini. They built a temple for Zeus since he was the one in charge of sending rain, apart from being the most powerful god. Zeus felt pleased by this gesture, brought the rain, and the nymphs returned, along with the island's beauty.
The first historical fact resources point out, apart from the prehistoric settlement discovered in the Agia Irini area, is the Persian invasion and the battles of Salamis and Artemisium. Kea fought along with Athens and was one of the few Cyclades islands to fight on the Greek side, along with Naxos, Tinos, and Kythnos. That is just an example of the historical relationship between Kea and Athens.
The final victory against the Persians came in 479 BC and took place at Plataea, where the 31 fighting states dedicated a trophy to Apollo that was said to be placed in the sanctuary at Delphi. This fact was confirmed in 1912 when the trophy (a column) was found in Constantinople. Once it was carefully cleaned, the names of the winning states - one of which being Kea - became intelligible. These were scripted on the bronze serpents decorating the column.
Kea was also the first Cycladic island to fight in the War of Independence. During the 20th century, establishments like the factory of Enamel were developed on the island; however, most of them gradually closed, resulting in the migration of many individuals. A small island between Kea and Attica, Makronissos, served as an exile location for communists during the junta of 1967-74.