A person generally commits the criminal offense of sexual assault of a child—regardless of whether the person knows the age of the child at the time of the offense—if the person (1) causes the penetration of the anus or sexual organ of a child by any means; (2) causes the penetration of the mouth of a child by the sexual organ of the person; (3) causes the sexual organ of the child to contact or penetrate the mouth, anus, or sexual organ of the person or another person; (4) causes the anus of a child to contact the mouth, anus, or sexual organ of the person or another person; or (5) causes the mouth of a child to contact the anus or sexual organ of the person or another person.

The naming and definition of the criminal offense of sexual assault of a child varies from state to state. These criminal offenses are generally located in a state’s statutes—often in the penal or criminal code.

In Illinois, the criminal offense of sexual assault of a child is addressed under the Illinois Criminal Sexual Assault statute, which is part of the Illinois Criminal Code of 2012. According to 720 ILCS 5/11-1.20 and 720 ILCS 5/11-1.40, a person commits the offense of criminal sexual assault if they commit an act of sexual penetration with a victim who is under 18 years of age when the act is committed, and the perpetrator is a family member, or the perpetrator is in a position of trust, authority, or supervision in relation to the victim. Additionally, under 720 ILCS 5/11-1.60, a person commits the offense of aggravated criminal sexual assault if they commit an act of sexual penetration with a victim who is under 13 years of age, among other aggravating circumstances. The law does not require the perpetrator to have knowledge of the child's age to be charged with the offense. These offenses carry severe penalties, including imprisonment, and are subject to Illinois state law and prosecutorial procedures.