Oak Harbor is a city located on Whidbey Island in Island County, Washington, United States. The population was 22,075 at the 2010 census. Oak Harbor was incorporated on May 14, 1915.

Whidbey Island is the largest of the islands composing Island County, Washington, in the United States, and the largest island in Washington state. Whidbey is about 30 miles (48 km) north of Seattle, and lies between 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. The state parks and natural forests are home to numerous old growth trees.