The Ilaiyen Archipelago was a chain of islands on the planet Sigma Niobe II, home to a group of Niobeans known as Ilaiyenai. As of the 23rd century, the Ilaiyen Archipelago was rarely visited by outsiders, and the few who did reported the natives' miraculous health and healing abilities.

In 2268, the steamship Enai-ra sailed to the Ilaiyen Archipelago from Reihairem, the Yemai Empire's closest port. (TOS short story: "As Others See Us")