Mouse Island is an island with an unknown governing body in the Geronimo Stilton universe. It is of course where the Stilton family reside with several other characters in the books, and the island where New Mouse City is located.
It consists of an unknown number of states, six major cities (New Mouse City, San Mouscisco, Mouseport, Mousefort Beach, Las Ratayas Marinas and Swissville) and has a total estimated landmass of 110000 square miles (284898.692 sq km). Its surrounding oceans consist of the Rodent Straights to its north, the Sea of Mice to the south, the Ratlantic Ocean to the east, and the Mousific Ocean on its west. The island shares no martime borders except for its own surrounding islands.