The first Rally, called the Black Hills Motor Classic, was held August 12-14, 1938. The first weekend in August was selected because it did not interfere with other established events held in surrounding communities such as Belle Fourche (rodeo) and Deadwood (Days of 76). Regional events were extremely important for social and economic reasons in the post depression Mid-west and as a good neighbor; Sturgis did not want to compete for those bodies and dollars.
As the event grew the "official" dates grew. The Sturgis® Motorcycle Rally™ is the first full week of August, Monday through Sunday, when preceded by a full weekend. This means that if 1 August falls on a Sunday the event would begin on the 9th with a full weekend preceding it. If 1 August would to fall on a Friday then the events official dates would be 4th through the 10th, the Monday through Sunday following the first full weekend in August.