What is a Ninth Cousin?

Do you want to know what a ninth cousin is? In this post, learn all about 9th cousins, including how many you have, how they are related, and more.

You will also find out:

The definition of a half-ninth cousin
The meaning of 9th cousin once and twice-removed
How many degrees of separation there are between ninth cousins
Whether 9th cousins are likely to share DNA
How to find ninth cousins

Most people are not likely to think about their ninth cousins very often. After all, these cousins are, by any definition, not closely related.

If you are into genealogy or family tree research, understanding how 9th cousins are related is very important. Plus, we have an incredible number of these relatives, as you will learn below.

There is a really good chance that you have met some of your ninth cousins, but you probably didn’t know it at the time! As you will find out in this post, we have so many 9th cousins that you might encounter a few while walking down a busy city street.

Let’s get started, shall we?

What is the definition of a 9th cousin?

Ninth cousins share 8th great-grandparents, also known as your great-great-great-great-great-great-great-great grandparents. Another way to think about it is that your 9th cousin is the child of your parent’s eighth cousin.

The common ancestor shared between ninth cousins is at least one 8th great-grandparent. It is possible to share only one 8th great-grandparent, or both (as in a married couple) 8th great-grandparents, with your 9th cousin.

You and your ninth cousins are descended from different children of your 8th great-grandparents. In other words, your 7th great-grandparents were siblings.

That’s a lot of “greats” to wrap the mind around!

Ninth cousin is also written as “9th cousin” or even just “9C”, for short. It is sometimes easier to use these terms instead of writing out the word “ninth” cousin, especially when you are referring to 9th cousins who are generations removed (see below), as it can get quite long.

What is a ninth cousin once-removed?

If you and your cousin might be ninth cousins, but don’t seem to be the same number of generations away from your 8th great-grandparents, then you might be a 9th cousin once-removed to each other. Your ninth cousin once-removed is the child of your 9th cousin, or one of your parent’s ninth cousins.

The common ancestor shared between ninth cousins once-removed, which is also written as 9C1R, is the 8th great-grandparents of the person most closely descended from the common ancestor. This is the same for 9th cousins twice-removed (9C2R).

What is a ninth-cousin twice-removed?

A ninth cousin twice-removed is the grandchild of one of your ninth-cousins, or the ninth cousin of your grandparent. We have many relatives who are related to us as a 9th cousin twice-removed.

In fact, most of our 9th cousins are likely to be cousins-removed, meaning that they are not the exact same number of generations removed from our shared ancestor.

Imagine that you discover a relative who is descended from your eight great-grandparent, but your 8th great-grandparent is their 10th great-grandparent. This person is your ninth-cousin twice-removed.

It works the same the other way around, too. For instance, a person who is descended from your 10th great-grandparent who is the 8th great-grandchild of that ancestor is also your 9th cousin twice-removed.

What is a half-ninth cousin?

A half-ninth cousin is a 9th cousin who is descended from only one 8th grandparent, instead of two 8th great-grandparents. For example, if your 8th great-grandmother passed away and her husband re-married, the descendants of the children of that new marriage will be your half-ninth cousins.

Are 9th cousins distant cousins?

Yes, ninth cousins are distant cousins. Cousins related at the 9th cousin relationship distance are very distantly related to each other, and are unlikely to feel a familial connection.

From a technical standpoint, cousins related more distantly than third cousins are all considered to be distant cousins.

With the increasing popularity of autosomal DNA testing and family tree research aided by technology, there is a growth in the number of relatives that we might be able to be in touch with. This means that more people are likely to have contact with a known 9th cousin than at any point in history, and it is possible for these very distantly related cousins to develop a close, friendly relationship.

However, ninth cousins are still distant cousins, no matter which way we look at it. One of the reasons that 9th cousins are distant cousins is because of the degrees of separation between them.

How many degrees of separation are there between 9th cousins?

There are twenty degrees of separation between ninth cousins. This is calculated by counting up ten generations to the 8th great-grandparents from one cousin and down ten generations to the ninth cousin, equaling a total of 20 degrees of consanguinity.

The number of degrees of separation help us understand why 9th cousins are distant cousins. If you consider that first cousins are only four degrees separated, you can see a big difference.

How many ninth cousins do you have?

Most people probably have over 1,000,000 ninth cousins. You could have even more, or a bit less, depending on economic and cultural factors affecting family sizes in the countries where your 9th cousins live.

If you put all of your 9th cousins together in the same area, you would need two cities the size of Atlanta, Georgia or one city the size of Austin, Texas, in order to fit them in one place.

That’s an incredible number of cousins. The sheer number of 9th cousins that we are likely to have is one reason why we can all be sure that we have probably met some of our 9th cousins.

Since we have so many 9th cousins, unless we live where no one else has ancestors from the same geographic region as we do, where are likely to know, or at least have known, someone who is our ninth cousin, even if we don’t know it.

Your mail carrier, colleague, friend, or even your spouse, could be your ninth cousin! That’s a crazy thing to imagine, but it’s true.

For example, if you live in Connecticut and your family has lived in the state as far back as you have been able to research, then chances are you are related to other people that you know – albeit very distantly.

It can be very difficult to trace a family tree going back to the 8th great-grandparents on all lines, which is why we are often unable to document how we might be related to some of the people we know, even it is seems like there should be a connection.

Why do we have so many ninth cousins?

The reason that we have so many ninth cousins is because we have a large number of ancestors at the 8th great-grandparent level. We have as many as 1024 eighth great-grandparents.

Imagine – that’s 512 couples who lived at least 250 years ago. Since then, at least ten generations of descendants have been born.

If each generation has 3-5 children, on average, you can see how the number of relatives would grow exponentially. By the time 10 generations pass, an incredibly large number of cousins exist descended from all of those 512 couples that you find in your family tree born hundreds of years ago.

Are 9th cousins blood related?

Most 9th cousins are not “blood related”, in that they likely do not share DNA with each other. In fact, we might only share genetic material with .0034 of our ninth cousins, which means that out of 1,000,000, we might only match the DNA of 3400 them – if they all were to take DNA tests.

Some people are surprised to learn that we don’t share DNA with all of our relatives, even those that are much more closely related than 9th cousins.

Because 9th cousins are very distantly related, and essentially considered to be “unrelated” by most people, it is completely acceptable for ninth cousins to marry each other. Some famous ninth cousin marriages include the marriage between Kevin Bacon and Kyra Sedgwick.

These two actors are ninth cousins once-removed to each other, even though they didn’t know it prior to their marriage. Sedgwick participated in the show Finding Your Roots with Henry Louis Gates, which is where she learned how she and her husband are (distantly!) related.

How to find your ninth cousins

The easiest way to locate your ninth cousins is to take an autosomal DNA test with a company that offers lots of DNA matches, and that shows matches who are not closely related to you. As you now know, it is unlikely to share DNA with a ninth cousin, which means we need to be able to find DNA matches that only share a small amount of DNA.

A top site for finding distant cousins is AncestryDNA. This is due to the large number of DNA matches that most customers have on the site, and the fact that customers can see genetic relatives who share only very small segments of DNA with them.

If we do share DNA with a ninth cousin, it is likely to be only a very small, single DNA segment.

Conclusion

I hope that this post helped you understand everything that you wanted to know about ninth cousins. My goal was to make this article a comprehensive source of information about 9th cousins and how they are related to us.

If you have any questions about something that you read in this post, or if you would like to share a story about meeting a ninth cousin, I would love to hear from you below.

Thanks for reading!