Tol Eressëa was designed as a kind of Isle of the Blessed inhabited by Elves, presenting a mythological backdrop to the Anglo-Saxon invasion of Great Britain. Tol Eressëa was conceived as a mythological equivalent of the island of Great Britain or Albion before the arrival of the Anglo-Saxons. Its main city, Kortirion, was located at the same place as Warwick, at the very centre of the island. Later, Tolkien dropped the identification of Tol Eressëa and Albion and made it an island situated far to the west, within sight of Valinor.
Source: Tol Eressëa – Wikipedia