A family tree with three generations.

Can You Marry Your First Cousin in Colorado?

Yes. Colorado law permits first cousins to marry without restriction. Someone called our office last week with a simple question about whether it was permissible to marry a cousin. While we unfortunately are not able to give out legal advice over the telephone (state bar concerns, plus our professional liability insurance carrier would have conniptions), there’s no harm in answering the question publicly (and anonymously) on this blog.

Pursuant to , the following relatives may not marry one-another:

  • Ancestor & Descendant (i.e. parent/child, grandparent/grandchild, etc)
  • Siblings (i.e. sisters or brothers)
  • Aunt/Uncle & Niece/Nephew, although this ban has an exception for “marriages permitted by the established customs of aboriginal cultures.”

In Colorado, the prohibitions are absolute, and do not depend upon whether one spouse is able to bear children, or whether the relative is half-blood or whole blood. Contrast that to some states, such as Arizona, Illinois & Indiana, where cousins are only permitted to marry if both of them are over 50, or one of them is infertile. Because Colorado has no such restrictions, there are occasional news reports about the state being a “destination” for first cousins from other states who wish to marry.

For a complete listing of the legality of marrying cousins in each state, see this Wikipedia article.

How About Birth Defects?

Does marrying your cousin increase the chances of children having birth defects? Yes. First cousins share about 12.5% of their DNA with one-another, and the concern over birth defects is what motivates some states to allow first cousin marriages only when the couple is incapable of having children.

recent study indicates that a child born to first cousins has a 4-7% chance of a birth defect, compared to 3-4% for other children. This was heralded as a reason why the concern over birth defects is overblown. But taking the average between both sets of numbers, the chance of a birth defect rises from 3.5% to 5.5% by marrying a first cousin. Still a small number, but that 2 point risk increase is a whopping 57% greater chance of a child with a birth defect – something most parents would rather avoid.

Do Any States Allow Incestuous Marriages?

No. While cousins are treated differently among the states, no state allows marriages between ancestors/descendants or siblings.

Moreover, most states criminalize sexual relations between such family members, even between consenting adults. In Colorado, for example, incest is a felony.  C.R.S. 18-6-301.

How About Royalty Marrying Within the Family?

Royal families have a long history of marrying other royalty to protect the royal bloodline or to cement foreign alliances. However there are a finite (and shrinking) number of royal houses, which necessarily meant marrying relatives (at least in the old days – now they marry us “commoners”). Usually the relatives were more distant than cousins, however.

Historians believe that the Habsburgs, once the most powerful royal family in Europe with an empire ancient Rome would have envied, were weakened and ultimately made sterile by inbreeding. In the 184 years they ruled Spain, nine out of eleven marriages were incestuous.

In ancient Egypt, pharaohs married almost exclusively within their own families, often to their sisters or brothers.

And who can forget one of the most infamous royal families, House Targaryen? For nearly 300 years, from Aegon I to Aerys II, the Targaryens ruled the Seven Kingdoms, and preserved their family’s bloodline with in-breeding. But we all know how that ended: the dragons died off, and the last Targaryen ruler (Mad King Aerys) went mad and was deposed by Robert Baratheon.**

** CAVEAT – When this blog was published, winter was ending in Colorado, but had yet to come in Westeros. We have to wait another three weeks for the much anticipated final season of Game of Thrones on HBO. It is entirely possible that a Targaryen will once again sit on the Iron Throne: Daenerys Targaryen and Jon Snow (rumored son of Rhaegar Targaryen and Lyanna Stark) are both strong contenders. And if they married each other and ruled together, they would be aunt and nephew – prohibited in Colorado, but not Westeros.

What Other Marriages Are Prohibited?

OK, back to Colorado. The other legal requirements for a marriage in Colorado are:

  • Both parties are over 18, or over 16 with the consent of both parents/guardians. C.R.S. 14-2-106(1)(a)(I).
  • Neither party is currently married or in a civil union (that would be bigamy).  C.R.S. 14-2-110(1)(a) & (1)(a.5).

Legal Effect of a Prohibited Marriage

A marriage which is void is void, and subject to annulment (called “declaration of invalidity of marriage” in Colorado. And marriages which were not prohibited, but entered into as a jest or date, based upon fraud, etc, may also be subject to annulment.

For complete details, see the Annulment in Colorado article in the Colorado Family Law Guide.

More Information

For more information about the requirement for a legal marriage in Colorado, see the Entering into Marriage article in the Colorado Family Law Guide, or if your situation involves a common law marriage, the Colorado Common Law Marriage article.