South Dakota Codified Laws
Chapter 05 - Time And Dates
Section 1-5-1.1 - Martin Luther King, Jr. Day established.

1-5-1.1. Martin Luther King, Jr. Day established.
The third Monday in January, to be known as Martin Luther King, Jr. Day shall be observed in this state as a legal holiday. Martin Luther King, Jr. Day is dedicated to the remembrance of Dr. Martin Luther King, Jr. and to the observance and appreciation of the various ethnic minorities who have contributed so much to the state and nation.

Source: SL 1986, ch 5; SL 1989, ch 5; SL 1990, ch 7, ยง3.