Adopted 12 December 1939 on 92/SE as labelled on BC Lands Map 2A, 1913.

Source: BC place name cards & correspondence, and/or research by BC Chief Geographer & Geographical Names Office staff.

The islands were named in by Captain George Richards of the Royal Navy survey vessel ‘Plumper’ after hearing that the British racehorse Thormanby had won the famous Epsom Derby earlier that year. Richards and his officers applied numerous race-related names to the area’s features, suggesting that they may have had a guinea or two riding on the winning horse. Most of the south island was pre-empted by Calvert Simson, storekeeper at Vancouver’s pioneer Hastings sawmill, in the early 1890s. He built a cabin and let his friends do likewise, and later developed a farm, which he ran with tenants. The Simson family donated much of the island as a provincial park in 1982. Another provincial park is located on a fine beach at the south end of North Thormanby Island. Elsewhere on this smaller island is Vaucroft Beach, where the BC Telephone Co maintained a hotel and summer camp for its employees in the 1920s.The Sechelt First Nation name for the islands is Sxwe̒lap.

Source: Scott, Andrew; "The Encyclopedia of Raincoast Place Names"; Harbour Publishing, Madeira Park, 2009.