To the east, it is separated from the mainland by the Swinomish Channel, and from Whidbey Island to the south by Deception Pass.

There are at least eight major lakes on Fidalgo Island which are named Campbell, Erie, Heart, Little Cranberry, Mud, Pass, Trafton/Crater, and Whistle.

At the time of European contact, Fidalgo Island was inhabited by the Samish and Swinomish peoples.

The Samish Indian Nation[2] maintains a presence in the area, with an administrative office in Anacortes.

Following this theme, Wilkes named the island's highest point Mount Erie.