The earliest (recognized...) references to the island of Atlantis are in Plato's works "Timaeus" and "Critias".
In his story, Critias describes the origins and form of Atlantis to Socrates and his guests.
The dialog of Timaeus is a continuation of Critias's tale, and delivers a more thorough history of ancient civilizations and mentions the state of Atlantis and its foreign relations, albeit briefly.
Although 'mainstream science' considers Atlantis to be a myth, Plato repeatedly
Plato's Timaeus & Critias
Over 11,000 years ago there existed an island nation located in the middle of the Atlantic ocean populated by a noble and powerful race. The people of this land possessed great wealth thanks to the natural resources found throughout their island. The island was a center for trade and commerce. The rulers of this land held sway over the people and land of their own island and well into Europe and Africa.
Atlantis was the domain of Poseidon, god of the sea. When Poseidon fell in love with a mortal woman, Cleito, he created a dwelling at the top of a hill near the middle of the island and surrounded the dwelling with rings of water and land to protect her.
Cleito gave birth to five sets of twin boys who became the first rulers of Atlantis. The island was divided among the brothers with the eldest, Atlas, first King of Atlantis, being given control over the central hill and surrounding areas.
At the top of the central hill, a temple was built to honor Poseidon which housed a giant gold statue of Poseidon riding a chariot pulled by winged horses. It was here that the rulers of Atlantis would come to discuss laws, pass judgments, and pay tribute to Poseidon.
To facilitate travel and trade, a water canal was cut through of the rings of land and water running south to the sea.
The city of Atlantis sat just outside the outer ring of water and spread across the plain. This was a densely populated area where the majority of the population lived.
Beyond the city lay a fertile plain surrounded by another canal used to collect water from the rivers and streams of the mountains. The climate was such that two harvests were possible each year. One in the winter fed by the rains and one in the summer fed by irrigation from the canal.
Surrounding the plain to the north were mountains which soared to the skies. Villages, lakes, rivers, and meadows dotted the mountains.
Besides the harvests, the island provided all kinds of herbs, fruits, and nuts. An abundance of animals, including elephants, roamed the island.
For generations the Atlanteans lived simple, virtuous lives. But slowly they began to change. Greed and power began to corrupt them. When Zeus saw the immorality of the Atlanteans he gathered the other gods to determine a suitable punishment.
In a single day and night of misfortune it was gone. The island of Atlantis,
its people, and its memory were swallowed by the sea.
(summary adapted from http://www.activemind.com/Mysterious/Topics/Atlantis/story.html)
Worldwide there are an estimated 500 mythological stories referring to a paradise island that sunk into
the sea due to disaster.
What a coincidence... :p