Incest is illegal in all 50 states, but the way the laws work is far from uniform. Every state criminalizes sexual contact between close blood relatives, and most prohibit marriage between them as well. Two states, however, do not prosecute incest between consenting adults, and penalties elsewhere range from a one-year maximum to life in prison depending on the relationship, the ages involved, and whether force was used.
The Two States That Don’t Prosecute Consenting Adults
New Jersey and Rhode Island are the outliers. New Jersey repealed its criminal incest statutes in 1978, and its current sexual assault law explicitly excludes consensual adult incest between people 18 or older. A 2024 bill tried to re-criminalize the conduct but died without advancing.1NJ Legislature. A4524 – Creates Crime of Incest
Rhode Island goes further, setting its threshold at 16. Consensual incest is not prosecuted there when both parties are 16 or older. In both states, though, the relationship cannot be formalized: incestuous marriages remain illegal and void.2Rhode Island General Assembly. Rhode Island General Laws 15-1-3 – Incestuous Marriages Void Everywhere else, the relationship itself is a crime regardless of consent.
Which Relationships Count
Every state’s incest law starts with close blood relationships: parents and children, grandparents and grandchildren, siblings, and aunts or uncles with nieces or nephews. These are prohibited universally, and the prohibition applies whether or not the people involved are adults. Half-siblings are treated the same as full siblings in every state that addresses the distinction. Georgia’s statute, for instance, explicitly lists “siblings of the whole blood or of the half blood” and applies the same punishment to both.3Justia Law. Georgia Code 16-6-22 – Incest
Beyond blood, the states diverge. Some reach relationships created by marriage. Colorado’s statute covers stepchildren age 21 or older alongside blood relatives. Michigan’s law reaches anyone related by blood or marriage within three degrees of kinship. Other states limit their statutes strictly to biological relatives and say nothing about stepparents, stepchildren, or in-laws. The practical result is that the same step-relationship can be a felony in one state and legally invisible in the next.
Adopted family members get more uniform treatment. Most states that address adoption in their incest statutes treat an adopted child as if they were a biological child of the adoptive parent, with the prohibition extending to adoptive siblings and other adoptive relatives.
First Cousin Marriage
First cousin relationships are where state laws split most sharply. Roughly 19 states and the District of Columbia allow first cousins to marry without restriction. About two dozen states ban it outright and treat such a marriage as incest. The rest allow it only under specific conditions, usually tied to the couple’s ability to have children.
Arizona, Illinois, Utah, and Wisconsin permit first cousin marriage when both parties have reached an age where childbearing is unlikely, or when one can prove infertility. Maine requires genetic counseling before issuing a marriage license to first cousins. Indiana allows it only when both cousins are over 65. Tennessee passed a bill in 2024 to ban first cousin marriage after nearly 200 years of permitting it under an 1829 statute. The national direction has been toward tightening these rules rather than loosening them.
Criminal Penalties
The sentencing spread across states is enormous. Delaware imposes the lightest maximum at one year. Most states fall between five and fifteen years for the baseline offense. Idaho, Kentucky, Montana, and Nevada authorize life imprisonment at the top end.
Kentucky shows how penalties scale with the circumstances. Consensual incest between adults is a Class C felony. If the act was nonconsensual or involved force, it rises to a Class B felony. If the victim was under 12, or the nonconsensual act caused serious physical injury, it becomes a Class A felony.4Kentucky Legislative Research Commission. Kentucky Revised Statutes 530.020 – Incest That pattern repeats across many states: a serious baseline that gets dramatically worse with aggravating factors.
When a minor is involved, prosecutors frequently stack additional charges like sexual abuse or statutory rape on top of the incest count. Those offenses carry their own penalties and can run consecutively. A position of authority over the victim, such as parent, guardian, or coach, also tends to push sentences toward the top of the available range.
Sex Offender Registration
Federal law sets minimum standards for sex offender registration through the Sex Offender Registration and Notification Act. SORNA defines a registrable sex offense as any criminal offense involving a sexual act or sexual contact with another person.5Office of the Law Revision Counsel. 34 USC Chapter 209 – Child Protection and Safety An incest conviction involving a minor meets that definition and triggers registration.
For consensual adult incest, SORNA excludes consensual sexual conduct from registration when the other person was an adult, with one exception: if that adult was under the offender’s custodial authority at the time, registration still applies.5Office of the Law Revision Counsel. 34 USC Chapter 209 – Child Protection and Safety Many incestuous relationships involve exactly that kind of power imbalance. States can also impose their own registration requirements that go beyond the federal floor, and many do.
Why Consent Is Not a Defense
In nearly every state, mutual consent between adults does nothing to reduce or eliminate criminal liability for incest. The crime is defined by the relationship, not by whether both people agreed. That makes incest different from most other sex crimes, where the absence of consent is what creates the offense. Here, the family connection itself is the prohibited element, and agreement between the parties doesn’t cure it. The exceptions are New Jersey and Rhode Island, where the legislature has effectively decided not to prosecute consenting adults.
When Lack of Knowledge Can Be a Defense
Not knowing about the relationship can be a real defense. This comes up more often than you might expect with adoption, anonymous conception, or long family estrangement. Courts have treated knowledge of the family relationship as an essential element of the offense, meaning the prosecution has to prove the defendant knew about the biological or legal connection.6Supreme Court of Wisconsin. Monroe County Department of Human Services v. Kelli B.
The prosecution also has to prove the relationship itself, typically through birth certificates, adoption records, or DNA evidence. Defense attorneys sometimes challenge that evidence or the credibility of witnesses claiming the defendant knew. A confession obtained through coercion can be excluded, which can gut the state’s case.
What Happens to an Incestuous Marriage
An incestuous marriage is not just illegal. In most states it is void from the start, or void ab initio, meaning it never had any legal validity and cannot be fixed later. That is different from a voidable marriage, which is treated as valid until a court says otherwise. A void incestuous marriage needs no court order to be invalid.
The practical consequences follow from that. A void marriage gives no basis for spousal inheritance, survivor benefits, or the other legal protections of marital status. Property acquired during the relationship is not automatically subject to marital division rules. If children were born, their legitimacy and custody are governed by separate family law provisions rather than by the invalid marriage.
When a couple legally marries in a state that permits their relationship and then moves to a state that prohibits it, the outcome is less clear. Courts generally recognize marriages that were valid where performed, but most states carve out a public policy exception for marriages they consider fundamentally offensive to their own laws. Close blood relative marriages almost always fall within that exception. First cousin marriages that were valid where performed have a better chance of surviving the move, especially if the new state doesn’t treat first cousin relationships as criminal incest.
Mandatory Reporting When a Minor Is Involved
Incest involving a child triggers mandatory reporting obligations across a wide range of professions. Federal law identifies incest with children as a form of child abuse that must be reported by covered individuals working on federal land or in federally operated facilities.7Office of the Law Revision Counsel. 34 USC 20341 – Child Abuse Reporting The federal list of mandatory reporters includes doctors, nurses, psychologists, teachers, school administrators, child care workers, social workers, law enforcement officers, foster parents, and commercial film and photo processors.
Every state has a parallel reporting law that applies beyond federal property, and most state lists mirror or exceed the federal one. Failure to report suspected child abuse is itself a criminal offense in most jurisdictions, usually a misdemeanor and occasionally a felony for repeat or egregious failures.
Religious communications get limited protection. Some states allow clergy to withhold a report when abuse was disclosed in a confidential confession and the clergy member determines the abuse is no longer ongoing. If the clergy member believes the abuse is continuing or could recur, the duty to report overrides the privilege.
Time Limits and Civil Remedies
Statutes of limitations for incest vary widely. Some states impose no time limit at all. Others set specific windows that depend heavily on whether the victim was a minor. A common approach pauses the limitations clock while the victim is underage and starts it when the victim reaches adulthood. Some states extend the window well into the victim’s 30s or 40s, reflecting the reality that many victims do not recognize or disclose the abuse until years later.
Victims can also pursue civil lawsuits against the perpetrator, separate from any criminal case. Common theories include assault, battery, and intentional infliction of emotional distress. Civil suits use a lower burden of proof than criminal prosecutions, preponderance of the evidence rather than beyond a reasonable doubt, and can produce monetary damages covering medical treatment, therapy, and lost income.