Adopted December 1920.

Source: BC place name cards, or correspondence to/from BC's Chief Geographer or BC Geographical Names Office

Named by Captain George Vancouver after James Johnstone, RN, master of the armed tender Chatham, who, exploring with the Chatham's cutter in July 1792, found for Vancouver this passage linking the Gulf of Georgia with the open Pacific to the north. Johnstone first visited this coast in 1786-89 aboard the trading vessel Prince of Wales, under Captain Colnett. No doubt it was because of the experience that Johnstone had gained on this private venture that Vancouver secured him his post on the Chatham. Johnstone became a captain in the Royal Navy in 1806, and later was a commissioner of the navy at Bombay.

Source: BC place name cards, or correspondence to/from BC's Chief Geographer or BC Geographical Names Office

Galiano and Valdes, who sailed through this strait about the same time as Vancouver, called it Canal de Descubierta ("Discovery strait").

Source: Walbran, John T; British Columbia Coast Names, 1592-1906: their origin and history; Ottawa, 1909 (republished for the Vancouver Public Library by J.J. Douglas Ltd, Vancouver, 1971)