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 Illinois, incest is defined as the offense of engaging in sexual relations or marriage between close relatives. Under Illinois law, specifically 720 ILCS 5/11-11, incestuous relationships are prohibited between a parent and a child, a step-parent and a stepchild, siblings whether by whole or half blood, an uncle or aunt with a niece or nephew, and between first cousins. Consent is not a defense to the charge of incest, meaning that even if both parties agree to the sexual relationship, it is still considered a criminal act. Incest is classified as a Class 3 felony in Illinois, which can result in a prison sentence of between 2 and 10 years, and a fine of up to $25,000. Additionally, a conviction for incest can lead to mandatory sex offender registration. It's important for individuals in Illinois to be aware of these regulations to avoid legal repercussions and to seek guidance from an attorney if they are facing allegations related to incest.