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Have you ever thought to yourself that it’s not worth the time to research your ancestor’s brothers and sisters?

If so, you’re not alone. A lot of people feel this way, especially when starting to research their family tree. Why research sideways when you can keep building your tree up instead of out, right?

A collateral ancestor actually has as much genealogical value as your direct ancestors. Because they share a common ancestor, by taking a closer look at them you may find the answers you need.

If you’re having difficulties tracing an ancestor, investigating these extended family members can be the solution to breaking through to the next generation.

This article discusses what are collateral lines in genealogy, and how to use them to further your family history research.

What is a collateral ancestor?

Your first question may be - who is a collateral relative, anyway?

Direct relatives are those you descend from, like your parents, grandparents, and great-grandparents. They are also called lineal ancestors.

Collateral kin are the extended family of your direct ancestors. You’re not descended from them, but you share a common ancestor.

Collateral relatives examples are::

Brothers and sisters
Cousins
Aunts and uncles
Nieces and nephews
In-laws

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Why you should research collateral relatives

It’s easy to get caught up in pursuing your direct line and pushing your tree back as many generations as possible. We all want to learn as much as we can.

Collateral relatives can give clues about those lineages when you hit roadblocks.

Researching sideways can not only help you identify clues to add more branches to your tree, it can bring to light family stories.

Questions like:

How large a family did your ancestor have?
Did any of their siblings die young?
Who attended school and for how long? Which siblings began working at an early age, and what type of work did they do?
Did any cousins, aunts, uncles, or other family live with your ancestor? If so, why?

Because they share a common ancestry, diving into these family members can give you important information about your ancestor that you may not be able to find in their records.

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How researching collateral lines can break brick walls

Stuck on an ancestor? When I can’t move past someone, I dig into researching their siblings and other family members.

Researching collateral lines can help you solve your family tree mysteries in a number of ways.

1) Maiden names. Finding the records for all of a couple’s children can help identify the mother’s maiden name. The same goes for researching the mother’s siblings. One of their records may hold the answer.

2) Birthplace. You can identify where an ancestor was born. Sometimes it can get confusing or be frustrating trying to figure out someone’s hometown or country. They may list different countries/states/towns of origin on different documents. They may not have created enough records to sort out the truth, but a relative's records might hold the key.

And sometimes they don’t list anything at all except a generic “Germany” or “Ireland”. I have an Irish branch that I couldn’t find where they came from. I found a tombstone for one of my ancestor’s brothers that said he was born in Gambonsfield, County Tipperary. From there, I was able to find a baptism record for my ancestor in that parish. I would never have found this if I hadn’t researched his siblings. This is the only thing that I’ve ever come across that gives a place of birth, for any of his family members.

3) DNA matches. One of the best resources for your genealogy toolkit is an Ancestry DNA test. If you know the surnames of your collateral lines, it can help you figure out how you’re related to your DNA matches.

This is especially useful for when your matches don't list family names (or only a few) on their profile. I’ve been able to identify how I’m likely related to someone, and on which branch just by looking at the surnames in their tree, even if the match has a very small tree or there are no common ancestors between us.

4) Name changes. Lots of families changed their names after arriving in the US. If your family’s last name was Anglicized or otherwise altered, collateral family can pinpoint their original name. Lots of families changed their names after arriving in the US. If your family’s last name was Anglicized or otherwise altered, collateral family can pinpoint their original name.

5) Sorting out people with the same name. If your ancestor has a common name or the family reused first names with every generation, collateral relatives can clear up who is who. This will ensure you’re researching the right line. (I’ve got 5 people named George Henry Burke in my tree!)

6) Pre-1850 records. Before 1850 (the first census to list all household members), there are fewer records documenting our family by name. Some disappeared over time and some were never created in the first place. Looking into all the collateral relatives increases your chances of moving back in your lineage.

7) Publishing. If you want to publish a family history, including collateral ancestors will make it more authoritative.

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How to do collateral relative research

Collateral ancestor research is a fabulous strategy for getting past roadblocks and uncovering more about your ancestor.

But the tricky thing is that it isn’t always obvious when someone is related to your ancestor. You may know at least some of your ancestor’s siblings or another family member, but there could be more that you don’t even know about, especially the further back in time you go.

Collateral kin can be hiding in plain sight. So, you’re going to want to identify possible relatives to add to your list of known family.

Begin your collateral research by looking for any other names that appear on the same records as your ancestor, whether they are obviously related or not.

Great resources to start with are:

Birth records
Marriage records
Death records
Censuses. Don’t forget to look at who lived next door to them!
Church records
City directories. Who was living in the same house or had the same surname?
Pension records. Who wrote affidavits in support of your ancestor’s pension?
Probate records. Who was involved in the estate or received a bequest?
Newspapers
Obituaries
Immigration records like naturalization papers and passenger lists
Social security card applications (SS-5 forms)
Deeds

Many of these have information on birthplaces, family members, maiden names, and other key hints to help you in your search. Using a genealogy records inventory can help you identify even more types of records to search for, as well as keep track of the ones you already have.

Note people who appear as witnesses to an event, such as a baptism, or family members that lived with your ancestor in a census enumeration. Even if someone was recorded as a boarder or roomer, they may in fact be a relative.

Record any details about them, if given in the record. For example, witnesses to a wedding in a parish register may give them place of residence.

Then, research your potential and known collateral relatives as you would your direct ancestors. Look for their vital records, censuses, and the other records I mentioned above.

Search for any connections to your ancestor and clues on how they could be related.

Where were they from? What are their maiden names? Did they migrate from place to place together?

This sideways research can be just the thing that will enable you to knock down a research roadblock to learn a wife’s maiden name or where your family was from.

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How collateral lines have helped my genealogy work

Besides the example I mentioned earlier about discovering my Irish ancestor’s place of birth in Ireland thanks to his brother’s gravestone, collateral research has helped me with one of the two biggest brick walls in my family tree.

These two roadblocks are Samuel Jones and his wife, Sarah Merrill. Both are very common names. I’m often researching all nine of their children, who also have common first names.

After a decade of looking, I recently got a hold of the Civil War pension file of their son, Henry.

Henry died in the war and to claim a dependent’s pension, Samuel had to prove he was Henry’s father. Sarah was dead by then, but two affidavits in the claim were from her cousins – my first clues ever on the Merrill family.

I’ve been digging into her cousins’ lineage, and I have very likely identified Sarah’s parents. I never would have found this incredible clue if I hadn’t taken the time to look into all their children and get a hold of every record I could.

Final thoughts

Sometimes it takes a roundabout route to track down your ancestors and add to your family tree. But by taking the time to research all of your direct ancestors’ siblings and other extended family, you’ll increase your chances of finding the answers you’re looking for!

Have you ever been able to solve a genealogy mystery by researching collateral relatives? Let me know in the comments!

Are you looking for help with your genealogy research?

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How and Why to Research Your Collateral Ancestors