▁South ▁Dak ota , ▁en act ed ▁a ▁criminal ▁ban ▁on ▁heter osex ual ▁and ▁hom osex ual ▁sod omy , ▁which ▁was ▁defined ▁as ▁" cr imes ▁against ▁nature ". ▁The ▁ban ▁prohib ited ▁anal ▁inter course , ▁regardless ▁of ▁whether ▁the ▁act ▁was ▁committed ▁in ▁private ▁and ▁cons ens ual . ▁P un ishment ▁could ▁vary ▁from ▁one ▁year ▁in ▁j ail ▁to ▁life ▁imprison ment . ▁In ▁ 1 8 7 7 , ▁the ▁maximum ▁penalty ▁was ▁reduced ▁to ▁ten ▁years ' ▁imprison ment . ▁In ▁ 1 9 1 0 , ▁the ▁definition ▁of ▁sod omy ▁was ▁expanded ▁to ▁include ▁fell atio ▁after ▁State ▁v . ▁Whit mar sh . ▁ ▁In ▁ 1 9 7 6 , ▁private , ▁adult , ▁cons ens ual ▁and ▁non - com mer cial ▁acts ▁of ▁sod omy ▁were ▁legal ized ▁with ▁an ▁age ▁of ▁consent ▁set ▁at ▁th ir teen ▁years . ▁The ▁age ▁of ▁consent ▁was ▁later ▁raised ▁to ▁fifteen ▁years . ▁ ▁Rec ogn ition ▁of ▁same - sex ▁relationships ▁ ▁South ▁Dak ota ▁vot ers ▁adopted ▁a ▁constitution al ▁am end ment ▁in ▁November ▁ 2 0 0 6 ▁that ▁defines ▁marriage ▁as ▁the ▁union ▁of ▁a ▁man ▁and ▁a ▁woman ▁and ▁prohib ited ▁the ▁recognition ▁of ▁same - sex ▁relationships ▁under ▁any ▁other ▁name , ▁such ▁as ▁civil ▁un ions ▁and ▁domestic ▁partners hip ▁agre ements . ▁Similar ▁restrictions ▁appear ▁in ▁the ▁state ▁stat utes ▁as ▁well . ▁ ▁On ▁June ▁ 2 6 , ▁ 2