- Whidbey Island is in an area that once lay under 3,000 feet of ice. Thirteen thousand years ago, receding glaciers gouged out the waterways and shaped the features of Puget Sound. Glacial moraine formed Whidbey Island, and like most Puget Sound landforms, it ranges no higher than 500 feet in elevation. The island varies from one to ten miles in width and its length extends nearly 40 miles in a north-south direction. Whidbey is the largest island in the Sound; in fact, after New York’s Long Island was officially declared a peninsula in 1985, Whidbey Island could claim to be the longest and largest island in the lower 48 states.