Incest is marriage or sexual relations between close relatives. The criminal offense of incest may also be known as prohibited sexual conduct. Laws vary from state to state, but incest laws generally prohibit marriage or sexual relations between (1) a person’s ancestor or descendant by blood or adoption; (2) a person’s current or former stepchild or stepparent; (3) a person’s parent’s brother or sister of the whole or half blood; (4) a person’s brother or sister of the whole or half blood or by adoption; (5) the children of a person’s brother or sister of the whole or half blood, or by adoption; or (6) the son or daughter of a person’s aunt or uncle of the whole or half blood or by adoption.

Lack of consent to sexual relations between such relatives is not an element of the crime, and persons may be guilty of the crime even if both parties consented.

Laws regarding incest or prohibited sexual contact vary from state to state and are generally located in a state’s statutes—often in the penal or criminal code. The crime is a felony offense in many states, with potential punishment of significant jail or prison time.

In South Dakota, incest is defined as marriage or sexual relations between close relatives, and it is considered a criminal offense. Under South Dakota Codified Laws (SDCL 22-22-19.1), incest occurs when there is sexual contact or sexual penetration between ancestors and descendants, siblings of the whole or half-blood, or between uncles, aunts, nephews, or nieces with whom there is a certain degree of blood relationship. This also extends to adoptive relationships that mirror these blood relationships. The law does not require a lack of consent to establish the offense; incest can be charged even if both parties consent to the sexual activity. Incest is classified as a felony in South Dakota, and those convicted may face severe penalties, including imprisonment.