The 1966 Southern 500, the 17th running of the event, was a NASCAR Grand National Series event that was held on September 5, 1966 at Darlington Raceway in Darlington, South Carolina. The transition to purposely-built racers occurred gradually begain in the early 1960s. Changes made to the sport by the late 1960s brought an end to the "strictly stock" vehicles of the 1950s; most of the cars were trailered to events or hauled in by trucks.