In antiquity, Irakleiá was named Arákleia and in medieval times Irakleítsa.
The history of the island begins from the 4th millennium BC, with its first inhabitants being the Cycladítes. Irakleiá remained on their possession up until 1000 BC.
During the first Byzantine years, in the 4th century AD, a castle was built behind Livádi beach, the runs of which can be seen today. However, due to the many piratic attacks, the island was abandoned and was not inhabited up until 1826 AD, by monks (the island belonged to the church of Panagía Hozoviótissa of Amorgós). In the 19th century, Irakleiá was finally settled by residents of Aigiáli town in Amorgós.
Ágios Ioánnis cave: A cave full of limestone, which can be visited with a tour guide. There is no asphalt road leading there, only a track road that turns to a difficult path.