South Dakota Codified Laws
Chapter 05 - Time And Dates
Section 1-5-16 - Day of the American Cowboy.

1-5-16. Day of the American Cowboy.
The fourth Saturday of July shall be known as Day of the American Cowboy. Day of the American Cowboy is dedicated to the protection, preservation, and promotion of the cowboy and Western heritage of the State of South Dakota, and honoring cowboys and cowgirls for their enduring contribution to the courageous, pioneering spirit of America. In keeping with the hard-riding work ethic of cowboys, the Day of the American Cowboy is a working holiday.

Source: SL 2014, ch 3, ยง1.