The largest grouping of islands in Washington are the San Juans, made up of 172 islands, in the upper Puget Sound. The most inhabited are the five islands that have regular Washington State Ferry Service connections with the mainland. These are the Guemes, Lopez, Orcas, Shaw, and San Juan Islands.

All islands are actually tops of mountains and, therefore, are rocky and surrounded by deep water. The islands are covered with small evergreens. Beaches are accessible at low tide.

Other islands in the Puget Sound, south of the San Juans, are characterized by high, sand bluffs and rocky beaches. Some have extensive farm lands. A state prison is located on McNeil Island.