For filming, there as a CGI collage comprising the island. I quote from the IMDB page: Scenery from Peddocks Island (initial island approach), Acadia National Park in Maine, Medfield State Hospital in Medfield, MA, and the Rice Estate at Turner Hill Country Club in Ipswich, MA were combined via CGI to create the imagery of Shutter Island as a whole. The large mountainous area of the island seen during the ferry approach was added in post-production and does not exist, but the decaying brick buildings on the lowlands are real ruins from Peddocks Island. The film takes place on Shutter Island.
