Can Third Cousins Marry Each Other? (2024) | How Are Third Cousins Related?

Third Cousin Introduction

Navigating the intricate web of family relationships can be a complicated endeavour, particularly when terms like “third cousin” come into play. This article will dive into the meaning and definition of what constitutes a third cousin, tracing the genealogy that links family members in this way. You will see how third cousins are related to each other, whether they are considered family, and how many such relatives the average person may have. In addition, the article will explore the DNA shared between third cousins, the phenomena of third cousins with no shared DNA, and distinctions such as third cousins once removed and half-third cousins.

What is a Third Cousin?

Third Cousin genetics ancestry

What is the Meaning of the Third Cousin?

A third cousin is a person who shares a common set of great-great-grandparents with you. In other words, your great-great-grandparents are their great-great-grandparents as well. This degree of cousinship signifies a generational gap within your family tree, with three generations separating you and your third cousin. Third cousins are considered distant relatives, and they share a relatively small amount of genetic material compared to closer relatives like siblings, first cousins, or even second cousins. 

How are second and third cousins related? Second and third cousins are related through their shared ancestry, but the degree of their relationship and the generational gap between them is different. Second cousins have a common pair of great-grandparents. In other words, their grandparents are siblings. This means there is a generational gap of two between them, as their common ancestors are their great-grandparents. On the other hand, third cousins share a common set of great-great-grandparents. Their great-grandparents are siblings, and their grandparents are cousins to each other. This creates a generational gap of three between them, as their common ancestors are their great-great-grandparents. This explains how second and third cousins are related.

How is a 3rd Cousin Related to You?

To clarify, we have explained the third cousin meaning it is the child of your parent’s second cousin. Your second cousin is the child of your parent’s first cousin etc. How are third cousins related? In most cases, your third cousin has a great-grandparent whose sibling is your great-grandparent. Therefore, you and your third cousin share a set of great-great-grandparents. Are third cousins blood-related? Yes, they are. This is because they share similar DNA profiles.

What is a Third Cousin Once Removed?

A third cousin once removed means that they are not within your generation. So, to you, your third cousin’s child would be your third cousin once removed. Your third cousin, to your parents, would be their second cousin once removed. In order to differentiate your third cousins once removed from your DNA match list, you have to tree build to determine that their parent is your direct third cousin.

On your DNA match list, you won’t see anyone listed as “removed” cousins by default (on some sites you are able to manually select the relationship). You won’t see the words “removed” or “half” by default because of the genetic range of cMs with which we share with our cousins.

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Are Third Cousins Considered Family?

Depending on the family, you might know your third cousins personally. Yes, third cousins are considered family. Even though third cousins are distant and they are not as closely related as first or second cousins, they are a part of your extended family tree. In many cultures and societies, third cousins are considered as family members, although distant ones.

The level of closeness or interaction between third cousins can vary widely depending on individual family dynamics and cultural norms, but they are generally acknowledged as part of the larger family network. Are third cousins distant? Yes, third cousins are considered distant relatives. The generational gap of three generations between third cousins results in a more distant relationship and they typically have minimal interaction or shared experiences in their day-to-day lives.

For most families, get-togethers are an exception, most other families, who do not have these close relationships likely do not know their third cousins or, they do know them as people, but they don’t know that they are cousins! Again, this scenario is common when families remain in the same geographic area but remember we do live in a small world! 

If you were not close with any family outside of your siblings and parents, you probably wouldn’t be able to pick out your third cousins from a lineup. Are third cousins blood-related? Third cousins are always considered to be relatives from a genealogical perspective, and there is about a 90% chance that third cousins will share DNA.

How Many Third Cousins Does the Average Person Have?

We can mathematically come to the conclusion that, on average, we have 190 third cousins (assuming each family has 2-3 children). We can have many third cousins depending on the size of our common ancestor’s family.

Read More:

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What is Fifth Cousin Once Removed?

What is a Third Cousin Once Removed?

How much DNA do Third Cousins Share?

Do third cousins share any DNA? Third cousins share anywhere from 30-230 cM (centiMorgans – the unit of measurement of shared DNA) with each other according to the Shared Centimorgan Project. The average amount of DNA shared with a third cousin is about 74 cM but this can be on such a wide range for a plethora of different reasons. Can third cousins share no DNA? It is possible that third cousins do not share DNA because of recombination. How much DNA do siblings share? If they are full siblings, they share approximately 50%. 

This chart shows how much-shared DNA there is between various relatives.


Relationship Average % DNA Shared Range
Identical Twin 100% N/A
Parent / Child 50% (but 47.5% for father-son relationships) N/A
Full Sibling 50% 38% – 61%
Grandparent / Grandchild
Aunt / Uncle
Niece / Nephew
Half Sibling
25% 17% – 34%
1st Cousin
Great-Uncle / Aunt
Great Nephew / Niece
12.5% 4% – 23%
1st Cousin once removed
Half first cousin
6.25% 2% – 11.5%
2nd Cousin 3.13% 2% – 6%
2nd Cousin once removed
Half second cousin
1.5% 0.6% – 2.5%
3rd Cousin 0.78% 0% – 2.2%
4th Cousin 0.20% 0% – 0.8%
5th Cousin to Distant Cousin 0.05% Variable

Can You Marry Your Third Cousin?

Third cousins sometimes find themselves asking the question of whether they can marry. It is generally legal for third cousins to marry in most jurisdictions, and the genetic overlap between third cousins is minimal, reducing concerns related to genetic issues that might arise in offspring. The most prevalent question at this point is usually, Can third cousins have babies?’ and the answer is, yes they can. Third cousin marriage defects have no more likelihood of happening than with any other person in a population. DNA gets literally diluted after the first cousin level so third cousin marriage birth defects are very unlikely to occur.


Can third cousins marry? Cultural norms and individual family traditions might influence perceptions of third-cousin marriages, but from a legal and genetic standpoint, such unions are typically permissible. 

So, can you marry your third cousin? It is always advisable to consult local laws and cultural practices to ensure that a marriage between third cousins aligns with societal norms and legal requirements in a particular region.

Fifth cousins share great-great-great-grandparents, linking them through a five-generation common ancestry. Despite the distance, connecting with fifth cousins can unveil interesting shared family history, showcasing the intricate complexity of family ties across generations.

Meaning Of Fifth Cousin, How Are They Related To You?

What is a Half-Third Cousin?

Earlier in this article we defined third cousins. A half-third cousin is when your great-grandparents are half-siblings and you would be sharing only one great-great-grandparent. Locating half-cousins must also be done by finding how they fit into your tree. Oftentimes, people will have more half-cousins than they realize because affairs cannot usually be traced genealogically but children born to affairs sure can be if their descendants have tested!

When we begin our research, we already have a clue where to begin. We may also have preconceived notions of who our ancestors were. When it comes to grandparents, especially if you knew them personally, it is a hard pill to swallow when you locate an individual with whom you share DNA that likely came out of an affair.

I always remind people of this – You knew them only in one or two phases of their life. You cannot pass judgment on them in their youth but you cannot claim, especially when genetic evidence suggests it, that they were not “that type of person”. It is so incredibly beneficial to genetic research to locate these removed and half-cousins, regardless if they are first, second, or third.

Through DNA testing, it is evident that they have some curiosities about the family’s history and it makes it a perfect opportunity to collaborate and to share copies of research and family stories or heirlooms that their direct line might not have even known about.

As soon as these relationships are built, it is very moving to have the realization that distant cousins can, unlike immediate family, sort of choose despite the phrase, “You can pick your nose but you cannot pick your family”. When it comes to distant cousins, you truly can build relationships and become quite close and, for others, you do not have to be friends if you do not want to be!

Demarcus Cousins the Third 

Demarcus Cousins III, commonly known as DeMarcus Cousins, is a professional basketball player renowned for his talent and versatility on the court. Born on August 13, 1990, in Mobile, Alabama, he has had a successful career in the NBA, showcasing his skills as a center for various teams, including the Sacramento Kings, New Orleans Pelicans, Golden State Warriors, and more. Demarcus Cousins the Third is recognized for his scoring ability, rebounding prowess, and physical presence in the paint. Despite battling injuries at times, he remains a formidable force in the league and a well-respected figure in the world of basketball.

Final thoughts

Locating how you relate to your DNA matches can only be beneficial for your family research. Third cousins are that perfect distance to prove and confirm your great-great grandparent’s lines. The best practice for keeping track of our third cousin (and more distant cousins) relationships, is building them in your family tree, or if they are on your DNA match list (on a certain site), you can edit their relationship to you or make a note about their relationship to you in order to prevent future confusion.



Can DNA testing identify third cousins?

Yes, DNA testing services can reveal third cousin relationships by analyzing shared genetic markers.

How common is it to know third cousins?

Knowing third cousins is less common than closer relatives, but technology and genealogy research can unveil these connections.

Is there a specific term for relationships beyond third cousins?

Relationships beyond third cousins are generally referred to by the number of generations that separate them, such as fourth cousins, fifth cousins, and so on.

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