Whidbey Island (historical spellings Whidby, Whitbey, or Whitby) is the largest of the islands composing Island County, Washington, in the United States. (The further large island is Camano Island, east of Whidbey.) Whidbey is virtually 30 miles (48 km) north of Seattle, and lies surrounded by the Olympic Peninsula and the I-5 corridor of western Washington. The island forms the northern boundary of Puget Sound. It is home to Naval Air Station Whidbey Island.

According to the 2000 census, Whidbey Island was house to 67,000 residents considering an estimated 29,000 of those breathing in rural locations. This increased slightly to 69,480 residents as of the 2010 census.

Whidbey Island is approximately 55 miles (89 km) long (if measured along roads traveled from the extreme north to extreme south), or just about 37 miles (60 km) when measured along a straight lineage from north to south, and 1.5 to 10 miles (2.4 to 16.1 km) wide, with a total land Place of 168.67 square miles (436.9 km²), making it the 40th largest island in the United States. It is ranked as the fourth longest and fourth largest island in the contiguous United States, behind Long Island, New York; Padre Island, Texas (the world’s longest barrier island); and Isle Royale, Michigan. In the confess of Washington, it is the largest island, followed by Orcas Island.

Whidbey Island was inhabited by members of the Lower Skagit, Swinomish, Suquamish, Snohomish and new Native American tribes. The Salishan publish for the island was Tscha-kole-chy. These were peaceful groups who lived off the sea and land, with fishing, harvesting nuts, berries and roots, which they preserved higher than the winter.

The first known European sighting of Whidbey Island was during the 1790 Spanish expedition of Manuel Quimper and Gonzalo López de Haro upon the Princesa Real.