Prior to being named after the Marquis of Mancera the island was known as Güiguacabin (from ühueñn, "whistle", or ühua, "maize", and cahuin, "party") to the indigenous Mapuches.

In his 1544 expedition Juan Bautista Pastene, made the island known for the Spanish and named it Imperial.

[4] In 1682, after Valdivia was badly damaged by a fire it was proposed to move the city to Mancera Island.

A similar proposal of moving the city to Mancera Island was done in 1721 in order to protect it against a potential British attack as Spain and Britain were at war.

[3] The decline in importance of Mancera Island in the fort system meant that by 1820, when Corral Bay was attacked by Patriots, it hosted only a small garrison and one battery of six cannons.