Complex sentence: The island has a year-round population of approximately 700 people, and is the largest in a chain of islands that makes up the small Wisconsin town of Washington, the other islands being Plum Island, Detroit Island, Hog Island, and Rock Island.
Split into simpler sentences: The island has a year-round population of approximately 700 people. It is the largest in a chain of islands which includes Plum Island, Detroit Island, Hog Island and Rock Island.