Tracing distant relatives, like third cousins, can be confusing. The relationship might seem far off, but it’s not always clear how to map these connections, especially as family trees get bigger and more complicated.
It’s easy to get lost trying to figure out how third cousins are related, how to track them down, or what tools to use to make sense of all the generations. It can feel overwhelming, and many people don’t know where to start.
In this guide, we’ll simplify what they are, show you how to find them, and give you practical tips and tools to make tracing distant relatives easier and less stressful.
» Find your third cousins by taking a DNA test
What is a third cousin?
Third cousins are people who share a set of great-great-grandparents. In genealogy, family relationships are defined by the most recent common ancestor. For second cousins, that ancestor is a great-grandparent. For fourth cousins, it’s a great-great-great-grandparent.
Each time the cousin number increases (e.g., second, third, fourth), the shared ancestor moves back to another generation.
To visualize third cousins, start with the common ancestor (great-great-grandparents) and trace both family lines forward to the individuals being compared. Alternatively, start with the individuals and trace backward to the common ancestor. Remember, third cousins are always in the same generation—they sit on the same “level” of the family tree.
» Learn more about first cousins once removed
How much DNA do third cousins share?
DNA inheritance, however, isn’t perfectly predictable. There’s an element of randomness. On average, third cousins share 0.781% of their DNA, or 53.13 centimorgans (cM). But, due to this randomness, about 10% of third cousins won’t share enough DNA to be detected as a match.
Because of this, researchers can’t rely solely on DNA data to confirm relationships. Instead, they need to use multiple sources and triangulate data to draw accurate conclusions.
» Learn more about Y-DNA tests and what you can learn from them
Finding family through third cousins
Tracing third-cousin relationships can help people reconnect with lost family branches or uncover unknown relatives. These connections are often undocumented, sometimes because they were intentionally hidden due to extramarital births or cultural norms of the time.
DNA research has revolutionized the discovery of such events, which were poorly recorded and might otherwise have remained hidden. Migration and adoptions—especially sealed adoptions—are two areas where records are often missing or nonexistent, particularly the further back in time you go.
When researching a specific individual or family line, genealogists frequently hit “brick walls”—points where proof is unavailable or even the previous generation is unknown. When this happens, it’s often helpful to shift focus and expand the search laterally.
For example, researching the siblings of direct ancestors can uncover the documentation originally sought. Sometimes, the needed records are linked to an ancestor’s sibling rather than the ancestor themselves. By broadening the search in this way, a dead end can turn into a breakthrough, as the necessary proof is often found just outside the original scope of research.
» Understand half and full relationships
How third cousins can prove your lineage
Verified third cousins can be invaluable in proving lineage, especially in cases like inheritance disputes. Researching these relatives often uncovers relevant documents that a narrow search on a direct ancestor might miss.
When a focused search hits a dead end, expanding to collateral ancestors—such as the siblings of direct ancestors and their descendants—can provide the necessary breakthroughs.
By widening your search, you not only increase the chances of finding useful documentation but may also discover that one of these extended family members holds valuable clues.
Family bibles, photographs, and other artifacts in their possession can offer critical insights and evidence for your genealogical research.
» Discover the difference between direct lineage and collateral relatives
How to find third cousins
Discovering third cousins not only opens up those specific individuals as possible organ donors for someone with serious medical conditions, but it opens up a whole family line of individuals who may qualify to be potential donors based on a genetic match.
MyHeritage offers several tools and features that can help you locate and connect with your third cousins. Here’s how you can use these resources effectively.
1. Start with your information
To find your third cousins, begin by creating a family tree on MyHeritage. You can input details about yourself, your parents, grandparents, and any known relatives. This foundational step is crucial because it uses the information in your tree to search for potential matches.
Once your family tree is established, is uses two key matching technologies:
- Smart matching: This feature compares your family tree with others on the platform, looking for shared names, dates, and locations. It can identify connections even if the data is discrepant.
- Record matching: MyHeritage automatically searches historical records (like census data and birth records) to find matches related to individuals in your tree. This can uncover new branches of your family that may include third cousins.
» Find out what happens when two people who share an ancestor reproduce
2. Use DNA testing
Taking a MyHeritage DNA test or uploading your existing genetic results from another service allows you to see a list of DNA matches, including potential third cousins.
The DNA testing feature provides an ethnicity estimate as well as insights into genetic relationships, which can help confirm connections to distant relatives.
MyHeritage also provides tools to help you interpret the centimorgans (cM) shared between you and your matches. Typically, third cousins share between 0-75 cM of DNA, so this information can guide you in identifying how closely related you might be.
3. Look for historical records and connect with matches
You can use MyHeritage’s historical record search engine to manually search for records related to your ancestors. By entering names, birth years, and locations, you may uncover documents that could lead you to third cousins or their ancestors.
If you find potential third cousins through Smart Matches™ or DNA Matches, MyHeritage allows you to reach out to these individuals. You can exchange information that may help clarify how you are related.
» Understand cluster and collateral genealogy
Additional tips for effective research
- Focus on one lineage at a time: Concentrating on either your paternal or maternal side can make the research process more manageable.
- Use shared ancestors: Identify common ancestors (like great-great-grandparents) as a starting point for tracing connections.
- Engage with relatives: Reach out to older family members who might have stories or documents that can enrich your understanding of your lineage.
» Find out what is a good match from a DNA perspective
Implications of third-cousin marriages
Contrary to popular belief, marriages between third cousins are not controversial anywhere in the world. In fact, many countries in the Middle East not only accept but also allow even closer relationships, such as marriages between first cousins. This makes third-cousin marriages even less contentious in those regions.
From a genetic perspective, third-cousin couples face no increased risk of genetic abnormalities compared to unrelated couples. On average, third cousins share only 0.78% of their DNA, which is minimal. This small amount of shared DNA means there is no higher risk of genetic birth defects in their offspring.
» Learn how to review DNA matches on MyHeritage
Challenges and solutions for genealogists tracing distant relatives
Mapping distant relatives, such as third cousins, comes with its own set of challenges. Tracing recent relationships is particularly difficult due to privacy laws that restrict access to information about living individuals. Many records about the living are not available to the public, and even public family trees often hide the identities of those still alive.
In some cases, privacy laws also limit access to records of the deceased for a certain period. For example, in Missouri, death certificates are sealed for 50 years after they are created. This makes it hard to trace the descendants of a common ancestor into the present.
On the other hand, the further back in time you go, the more likely it is that historical records will be missing, damaged, or inaccurate. This creates another layer of difficulty in piecing together family connections.
Another hurdle is tracking surnames through generations. Surnames are often inconsistent, with frequent spelling variations. Immigration and cultural shifts can also alter surnames in unpredictable ways, making it harder to follow family lines.
Wrapping up the third-cousin mystery
Tracing third cousins may seem daunting at first, but with the right approach and tools, it’s totally doable. By understanding the relationship and following the steps outlined in this guide, you’ll be able to connect the dots in your family tree and uncover new branches you never knew existed.
So grab your family records, dive into the search, and enjoy the journey of discovering your distant kin!
» Find your third cousins by taking a DNA test
