In the majority of states in the United States, incest is illegal. The punishments associated with engaging in an incestuous relationship vary by state. In many cases, incest is not revealed to outside parties, so therefore, the parties involved are not prosecuted. In the states of New Jersey and Rhode Island, incest between adults is legal. However, neither state permits marriage. Penal code 285 PC is the California statute that defines the crime of incest. Under this section, Incest – defined as marriage or sexual relations between close relatives – is prosecuted as a felony. 1. The types of relatives who may not legally marry or have sex with each other are: Parents and children;