Campobello , island, 9 mi (14.5 km) long and 3 mi (4.8 km) wide, in Passamaquoddy Bay, N.B., Canada, just off the coast of Maine. The island passed to Canada by the Convention of 1817. President Franklin Delano Roosevelt had a summer home in Welchport, the main settlement, for many years. It is now preserved in Roosevelt-Campobello International Park.