What Does Half Cousin Mean?

Are you filling in your family tree and aren’t too sure what a half-cousin is? Perhaps someone has reached out to you claiming to be a half-cousin and you don’t know what that means?

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Or perhaps you are curious and want to know more? Whatever your reason might be, we have the answer for you! 

We know how confusing family trees and genealogy can be, especially if you are new to it all! There are so many different terms and phrases that it can be difficult to understand who is related to who on your family tree.

You find yourself overwhelmed, frustrated, and unsure of where to get this information from.

Everywhere you turn seems to be overly complicated, unable to give you one clear answer. 

Well, no more! Today we are here to give you the answers that you need. Keep reading to find out what a half-cousin is, how to spot them on your family tree and what their relationship could be to you! Get ready to become a family tree expert. 

What Is A Half-Cousin?

Let’s dive straight into it! A half-cousin is the child of a half-uncle or half-aunt. Half-cousins come from descendants of half-siblings and we commonly see these after remarriage or a couple separating and cohabiting with different partners. 

Half-cousins will be descended from half-siblings that share one grandparent. Would you like an example? Here you go! Let’s take for example your mother.

If her mother (your maternal grandmother) passed away and your grandfather remarried, any more children he had would be your mother’s half-sibling. 


They would then be your half-aunt or half-uncle. As you and your cousin’s parents, Any children they had would then be your half-cousin. Half cousins are more common than you think.

With many people remarrying after divorce or the death of a spouse, families are becoming more and more blended. And while we are seeing the dynamic of families change, we need phrases that can best describe them. 

Half-siblings, aunts, uncles, and cousins are one way to do this. They share one relative rather than a set (of parents) and therefore, share half the amount of DNA.

While half-siblings and other half relatives do not share a full set of parents or grandparents, it is worth noting that it doesn’t lessen their bond as a family. 

Families come in all shapes and sizes. They always have, it’s just that these days there is more acceptance towards them. And the genetic bond shared between these relatives does not determine the emotional bond that they share.

You can be just as close to your half-cousins as you can with your full cousins. It does not change anything if you don’t want to and it is important to remember that. 

That said, the term half-cousins is a useful one when looking at genealogy. If you performed a DNA test, then the phrase half-cousin will come in handy! Your half-cousin tends to share half the expected amount of DNA we see with full cousins.

So if the DNA shared with your cousins is lower than you thought, that could be a half-cousin! 

Suddenly, there is more work that needs to be done on your family tree to show the half relation shop. It can even reveal secrets in your family, especially if no one was aware that they were half-siblings (which leads to the creation of half-cousins).

While that can sound like a sordid scandal reserved only for lunchtime soap dramas, in previous generations, half-siblings were kept secret, especially if they were the result of an affair. When you search for half-cousins, you never know what you will uncover. 

Now that we have established what a half-cousin is, let’s take a look at how they relate to first cousins, second cousins, third cousins, and so on. 

What Is A Half-First Cousin?

Let’s start with your half-first cousins. These are people that share one grandparent, compared to full cousins that share two grandparents. This is like the example that we gave you earlier and happens when half-cousins’ parents are half-siblings. 

Half-first cousins are extremely common and most people likely have them! If your parents have half-siblings, then their children are your half-cousins. Think about your family, do you have any half-first cousins? 

If you aren’t sure, we’ve got an example that we think will help! Think of your grandmother and pretend that she was married twice (she might well have been for all we know).

If she had your father as part of her first marriage and your aunt from her second marriage then they would be half-siblings. They would have the same mother, but different fathers. 

Any children that your father and aunt had with their partners would be half-first cousins. On a family tree, you would see two unions for your grandmother, hopefully not at the same time! 

Under the union for the first marriage, you would see one-half sibling (in this example, your father). Under the second union, you would see another half-sibling, your aunt. Underneath your father and aunt respectively would be yourself and your first-half cousin.

In situations of divorce, loss of a partner, or adultery, we see half-siblings and half-first cousins! They are more common than you think, and often, the knowledge that your cousin is a half-cousin is unlikely to impact your relationship with them. 

What Is A Half-Second Cousin?

Next, let’s take a look at second cousins. We all have four sets of great-grandparents, and this is where second cousins come from.

A second cousin will share one out of your four sets of great-grandparents, for example, you might have the same great-grandmother on your maternal grandmother’s side of the family. 

And you can get half-second cousins too! You get a half-second cousin when one of your great-grandparents remarries and has a child with their second partner. Remember, your relatives don’t need to be married to have children!

Your great-grandparent might have cohabited or had an affair that bore a child. When looking at older generations, affair or remarriage is usually the most common cause of these children, as divorce was not common. 

Let’s have an example of this! Say your great grandmother married young and had three children before her husband passed away. After the loss of her husband, your great-grandmother remarries and has another child with her new husband. These four siblings now share one parent, their mother, making them half-siblings.

That child now has three half-siblings and they have a half-sibling. Now, any children that the fourth child has will be first-half cousins with their half-siblings. The children of their children will then be half-second cousins. 

It is worth noting that any children or grandchildren of the first three siblings will all be full first and second cousins as they all share the same grandparents and great-grandparents, it is just their relationship with the fourth child that is a ‘half’ relationship. 

Do You Know Your Second Cousins?

Depending on how close your family is and how many children your grandparents and great-grandparents had, you might know some or all of your second cousins. These could be full or half-second cousins and you might have grown up in the same area, or connected with them while completing a family tree or at a family reunion. 

It is also possible that you don’t personally know the children of second cousins, or second cousins once removed as they are known. If the children of your great-grandparents scattered or did not remain in contact, then it is unlikely that their children and grandchildren kept in contact with one another too.

It might be that these are people you meet at family reunions or events like weddings or funerals. 

Second cousins and half-second cousins can be a confusing relationship and one that people often misunderstand. To help avoid that it is worth remembering that these cousins come from a great-grandparent, whether it is your maternal or paternal side of the family. 

The great-grandparent will have had two marriages or relationships that bore children. The children are then half-siblings if they only share one parent. The children of these half-siblings are then half-first cousins and their children half-second cousins.

As long as you remember that second cousins come from your great grandparents and the children they had, you can track your family tree with ease and find these cousins. 

What Is A Half-Third Cousin?

A half-third cousin is someone that shares one great-great-grandparent with you rather than two great-great-grandparents that full third cousins share.

Most of us will have eight sets of great-great-grandparents (a set of parents for all four of your great-grandparents) and the people that share one set are your third cousins. 

If you only share one great-great-grandparent instead of a set, then the person you share them with is your half-third cousin. Now, it can be confusing to go a few generations back and try to chart your third cousins, so we recommend working backward from you and your parents, adding in aunts, uncles, cousins, and grandparents until you hit your great-great-grandparents.

A good way to think about it is to remember that you have sixteen great-great-grandparents and if you share just one of these with a cousin, they are your half-third cousin. If you share a full set, then you are full third cousins. 

Finding A Half-Third Cousin

So, what does a half-third cousin look like on a family tree? Well, let’s start at the top and work our way down to help you make some sense of it. For our example, we are sticking to one or two children from each marriage to keep it simple, but it’s worth noting that your family tree might be larger than the one we are creating. 

So let’s start with a great-great-grandfather who married twice. In his first marriage, he had a daughter and a son in his second marriage. These children are half-siblings and one of these will be your great-grandparent.

The children of the son and daughter are half-first cousins, with one of them being your grandparent. The children of your grandparents are then half-second cousins, leaving you to be half-third cousins with any children that come from the original half-siblings side of the family.

Finding your half-third cousins can be done with family trees on sites like Ancestry, by speaking to relatives to learn more about your family tree. DNA testing can also identify blood relations, but you would have a low genetic match to these half-third cousins as the blood relation is removed. 

What Is A Half-Fourth Cousin?

Finally, we come to half-fourth cousins. They come from sharing one of your great-great-great-grandparents.

If one of these great-great-great-grandparents remarried and had children with another partner, their descendants will be your half-fourth cousin. It is quite likely that you have some of these in your family. 

To find your great-great-great-grandparents, you are moving through a few generations to a time where war was rife along with illness, poor health, and a lack of access to medicine. This meant that many people were widowed and are likely to remarry and have children with another partner, resulting in present-day half-fourth cousins for you!

And if we thought that a half-third cousin was removed from your shared blood relatives, then for half-fourth cousins, it is even further! From a genealogy perspective, there is a 50% chance that you share no DNA with a fourth cousin whether they are full or half cousins. 

This means you cannot rely on DNA testing here to identify fourth cousins. Instead, it would be better to turn to family tree sites like Ancestry or local and national archives that can help identify relations to you and build a family tree full of half and full cousins. 

Final Thoughts 

And there we have it, half-cousins are cousins that only share one relative with you as opposed to two. Whether this is a grandparent, great-grandparent, great-great-grandparent, or great-great-great grandparent, your family likely has some half-cousins tucked away on the family tree somewhere! 

Finding them can be done through family trees, DNA testing, or speaking to your relatives to fill in any blanks. While you might have to dig to uncover an illegitimate child somewhere a few generations.

Use these genealogy forms to stay organized as you discover your family history!

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