Mount Desert Island (often abbreviated MDI), in Hancock County, Maine, is the largest island off the coast of Maine. With an area of 108 square miles (280 km²) it is the 6th largest island in the contiguous United States. Though it is often claimed to be the third largest island on the eastern seaboard of the United States, it is actually second behind Long Island (and ahead of Martha's Vineyard.) The island has a year-round population of approximately 10,000, although it is estimated that two and a half million tourists a year visit Acadia National Park on the island. The island is home to numerous well-known summer colonies such as Northeast Harbor and Bar Harbor.