Sonora Island is one of the outer islands (without ferry service) of the Discovery Islands of British Columbia, Canada. It is located at the eastern end of Johnstone Strait and the northern end of Discovery Passage within Electoral Area C of the Strathcona Regional District. The island includes Thurston Bay Marine Provincial Park on the west side of the island (accessible only by sea) and a resort on the east side of the island. The island is the location of the Sonora Resort, and Cathers Cove- the only rentals on the island.