S.D. Codified Laws § 1-5-1
The first day of every week, known as Sunday; the first day of January, commonly known as New Year's Day; the third Monday in January, commonly known as Martin Luther King, Jr. Day; the third Monday in February, the anniversary of the birthdays of Lincoln and Washington; the last Monday of May, commonly known as Memorial Day; the nineteenth day of June, commonly known as Juneteenth; the fourth day of July, commonly known as Independence Day; the first Monday in September, commonly known as Labor Day; the second Monday in October, commonly known as Native Americans' Day; the eleventh day of November, known as Veterans' Day; the fourth Thursday in November, commonly known as Thanksgiving Day; and the twenty-fifth day of December, commonly known as Christmas Day; and every day appointed by the President of the United States, or by the Governor of this state for a public fast, thanksgiving, or holiday shall be observed in this state as a legal holiday.
If the first day of January, the nineteenth day of June, the fourth day of July, the eleventh day of November, or the twenty-fifth day of December falls upon a Sunday, the Monday following is a legal holiday and shall be so observed; and if any such day falls upon a Saturday, the preceding Friday is a legal holiday and shall be so observed.
SDCL 1-5-1