Posted by Julie Granka on March 14, 2014 in AncestryDNA, Holidays

At AncestryDNA, we’re celebrating Saint Patrick’s Day a little differently than most. We’re exploring how we can use genetics to study Irish heritage in the U.S.

Throughout our nation’s history, millions of individuals from Ireland planted new roots here in the United States. While hundreds of thousands of Irish immigrants arrived in the 1600’s and 1700’s, more than two million arrived in the mid-19th century – most to flee the “Potato Famine” that destroyed crops and led to widespread starvation in Ireland.

Historical records and census data tell us that many Irish settled in the Northeastern region of the United States. By 1850, people from Ireland made up over a quarter of the population of Boston, Philadelphia, Baltimore, and New York City.

Let’s fast-forward to the 21st century and discover where descendants of Irish immigrants now live in the United States – using DNA. We may help to explain why you do (or don’t) see many people around you wearing green.


Using DNA

At AncestryDNA, all customers receive a unique estimate of their “genetic ethnicity” – where in the world their ancestors may have lived hundreds to thousands of years ago – based on their DNA. For example, an AncestryDNA ethnicity estimate can tell someone how much of their DNA likely came from Ireland – anywhere from 0% to 100%.

The ethnicity estimate can give a fascinating glimpse into one’s past: Americans with some Irish ethnicity may have an ancestor who immigrated to the U.S. from Ireland.

Based on AncestryDNA ethnicity estimates for over 300,000 AncestryDNA customers*, the AncestryDNA science team set out to discover the “most Irish” regions of the U.S.


States with the highest Irish ancestry

First, for all AncestryDNA ethnicity estimates of people born in the same state, we averaged their fractions of Irish ethnicity. Then, we found the U.S. states whose residents have the highest, and lowest, amounts of Irish ancestry.

On the map are the top five states with the highest average Irish ancestry.  Massachusetts is #1, and all of the other top states are also in the Northeast.

IrishMap_USASound familiar?  As we mentioned at the start, Irish immigrants disembarked primarily in the Northeastern region of the U.S., particularly in Boston.

Genetics and history agree!  Using only DNA, we find that many of the present-day descendants of Irish immigrants still live in and are born in the Northeast.

Since descendants of Irish immigrants have made their way all over the country, Irish ancestry is found in many states outside of the Northeast as well.  But some areas of the U.S. seem to be less commonly settled by people of Irish descent.  The states with the lowest average Irish ancestry are North Dakota, Wisconsin, Hawaii, and Minnesota, all with less than 12% average Irish ancestry.


Cities with the highest Irish ancestry

Which U.S. cities have the highest amounts of Irish ethnicity based on DNA?

To answer this, we averaged the Irish ethnicity of all AncestryDNA customers born in a given city.

In the map below, the darker the green, the higher the average Irish ancestry of the city (bigger circles mean that more AncestryDNA customers were born there).  You may not see your city listed because we only looked at the top 50 cities with more than about 400 AncestryDNA customers.

R version 2.15.1 (2012-06-22). Made using googleVis-0.4.7.


Here’s a list of the top 10 cities with the highest average Irish ethnicity:

Top 10 Cities

City Average Irish Ethnicity
Boston, MA 34.3%
Philadelphia, PA 22.3%
Pittsburgh, PA 19.6%
Fort Worth, TX 19.6%
Birmingham, AL 19.3%
San Francisco, CA 19.0%
Tulsa, OK 19.0%
Springfield, MA 18.9%
Oklahoma City, OK 18.4%
New York, NY 18.3%


The “greenest” city by a large margin is Boston – with an average Irish ethnicity of 34%!  Other top cities are Philadelphia, Pittsburgh, and Fort Worth.

As before, many of these cities are in the Northeast.  Millions of Irish immigrants set their roots there – and genetics shows that many of their descendants have not strayed far.  But the fact that cities outside the Northeast are on this list shows that Irish immigrants also settled in non-Northeastern big cities, and that some of their descendants moved elsewhere.



What about the cities with the lowest average Irish ancestry?  It might not be a surprise that none of them are in the Northeast.

Bottom 10 Cities

City Average Irish Ethnicity
Milwaukee, WI 10.3%
Toledo, OH 13.0%
Minneapolis, MN 13.1%
San Antonio, TX 13.3%
Salt Lake City, UT 13.3%
Los Angeles, CA 13.6%
New Orleans, LA 14.0%
St. Paul, MN 14.2%
Detroit, MI 14.3%
Chicago, IL 14.4%


While there are likely some people in these cities with Irish heritage, there aren’t as many as in Boston – suggesting that fewer Irish immigrants settled in these areas.

And in cities such as Los Angeles where Irish immigrants are known to have lived, the signal of Irish ancestry has likely been lessened by an influx of immigration of individuals of other ancestries.




So where’s the best place to celebrate St. Patrick’s Day?  The “Top 10” list might be a good place to start.  In fact, Bostonians have been celebrating with a St. Patrick’s Day parade since 1737, New Yorkers since 1762, and Philadelphians since 1771.


Genetics of Irish Americans

Although everyone’s Irish on St. Patrick’s Day, AncestryDNA can tell someone whether they have Irish heritage the other 364 days of the year– and whether they might have had an ancestor who immigrated from Ireland to America.  We’ve found that people from states and cities of the Northeast, where many Irish originally started their new future in the U.S., have the highest amounts of Irish ancestry.

While U.S. census data based on “self-reported” Irish ancestry shows similar patterns, our study is unique since we’re using only genetics.  This allows us to incorporate information about “Irishness” from people who may not self-identify as Irish, but still seem to have Irish heritage based on DNA.  Both views of one’s ancestry are equally important.

So even if your AncestryDNA results don’t reveal your Irish heritage, there’s no reason not to wear green and seek out the best corned beef and cabbage.  Now you know where to look for it.


*All AncestryDNA customers in this study consented to participate in research.


Julie Granka

Julie has been a population geneticist at AncestryDNA since May 2013. Before that, Julie received her Ph.D. in Biology and M.S. in Statistics from Stanford University, where she studied genetic data from human populations and developed computational tools to answer questions about population history and evolution. She also spent time collecting and studying DNA using spit-collection tubes like the ones in an AncestryDNA kit. Julie likes to spend her non-computer time enjoying the outdoors – hiking, biking, running, swimming, camping, and picnicking. But if she’s inside, she’s baking, drawing, and painting.


  1. skm

    Oops. The state of Minnesota is abbreviated MN, not MI. See errors on “Bottom 10 Cities” chart. There are no cities of Minneapolis or St. Paul in the Great State of Michigan, which has the postal abbreviation of MI. Thanks in advance for your corrections.

    • Julie Granka

      We have updated the post with the proper abbreviations. Thank you so much for catching our error.

  2. skm

    Hi, it’s me again! I overlooked “Detroit, IL” because I knew that such a place exists, I thought it might be a big suburb of Chicago–nope. I looked it up for fun, turns out it has a population of about 93 individuals, not a large place at all. Is this supposed to be “Detroit, MI”, the Motor City, with a population of 701,000? I learned something about the “other” Detroit today, thanks! 🙂

  3. Julie,

    Thanks for your research in this area and being able so well to translate all the science in this area to “lay” people terms.

    I hope you, Ken, and others at AncestryDNA will continue this style of reporting your research findings.

    Legend has it that Saint Patrick was kidnapped in England over 1700 years ago and taken to Ireland as a slave for an Irish slaveholder.

    Fast forward to America about 200 years ago and we find many African Americans today are descendant from male Irish American slaveholders. Is there a chance in 2015 you could do an update of this St. Patrick’s Day posting also showing the Top 10 Cities for Irish-African-American ethnicity?

    As a suggestion from a customer, could AncestryDNA consider forming an “African American Advisory Board” and working with skilled and lay Genetic Genealogists in this area?

    Here’s an article which you and others may like:

  4. Marcia DeHaven

    Wow! I can’t believe Savannah, Georgia wasn’t included somewhere in the St. Patrick’s Day – Irish survey. Of course, maybe most Southerners are just considered Scotch Irish?

    • Julie Granka

      Thanks for your interest, Marcia. In this study, we only looked at the 50 cities of the United States with the most AncestryDNA customers born in that city (greater than about 400 customers). The reason that Savannah, Georgia was not included is that not enough AncestryDNA customers were born there. So, we have not calculated a ranking for Savannah.

  5. George Jones

    In 2012, the US Census Bureau DEMOGRAPHICALLY reported that that the Boston Metro Area Population was ~24.1% of “Irish Ancestry”. This is about 1,118,000 persons who “self reported” some degree of Irish Ancestry.
    In 2014, GENETICALLY reported a 34.3% statistic for “Average Irish Ethnicity” in Boston as a City.
    How can this 10.2% discrepancy best be explained?
    1. reported their statistics on a “Boston City” basis whereas the US Census Bureau reports on a larger and more disperse “Boston Metro” basis? For instance, many students at MIT and Harvard are of Asian (Chinese, Indian, Korean) Ancestry.
    2. There is a very significant percentage of the “Boston Metro” population not completely aware of their ancestral genetic makeup and consequently have higher degrees of “Hidden Irish Ancestry”?
    3. The Educational Attainment of the DNA Irish Ethnicity test takers is considerably higher. The US Census says 19.1% of the Boston Metro Irish Population is reported to have a Graduate or Professional Degree? This is likely higher for the average Boston testee.
    4.There is an Irish Leprechaun jiggling with the algorithms and statistics?
    5. All of the above.

    • Julie Granka

      Hi George, thank you for your insightful comment. The answer is somewhat a combination of the options 1, 2, and 3 that you provide. First, we are looking at birth locations, not current locations. These birth locations are based on family trees created by customers, where location definitions may or may not be consistent with those used by the census. Second, it is possible that our view of the United States is slightly different than the census’ view, since we are only examining AncestryDNA customers.

      The most important reason to explain this discrepancy is the difference between what the census is measuring and what we are measuring. The census estimate is an estimate of the proportion of people in Boston who have Irish ancestry. Ours is an estimate of the average proportion of Irish ancestry across all people born in Boston. These numbers can be different because self-reported ancestry and genetic estimates of ancestry may be different. As you suggest, individuals may have some Irish ancestry even if they do not identify themselves as Irish.

      Take this fictitious example:

      25% of people born in Boston self-report as Irish, and they all have 100% Irish ancestry.
      25% of people born in Boston have 30% Irish ancestry and don’t self report as Irish.
      50% of people born in Boston have only 5% Irish ancestry and don’t self report as Irish.

      Census result = 25% of people self-report as Irish
      Our result = average Irish proportion of 35% (.25*100 + .25*30 + 0.50*5)

      So while 25% of people in Boston self-report as Irish, the average amount of Irish ethnicity among all Bostonians can in fact be higher. Thank you for helping to clarify this important point. There are no leprechauns jiggling with the statistics here!

  6. Justin Turner

    Hi Julie I am hoping you can recommend some reading for me – I don’t really have a background in genetics. I have friends who are very enthusiastic about genealogy projects, but despite all of this great technology and efforts they seem to think there are real scientific boundaries to different populations that they think go back to the beginning of time. My intuition is this is not correct – we all have a common ancestor (or common group of ancestors but the group was so small it is functionally one point in time) and any classification of their descendants into separate groups – whether self defined or not – is ultimately contentious. That just seems like common sense! I am really hoping you can recommend some reading material so that I can develop a little more sophisticated appreciation about how people talk in a scientific manner about ‘populations’. I really don’t want a naive perspective here… I worry that my peers interest in genetics is perpetuating essentialist ideas about groups, if you will, and I don’t have the experience to talk about this properly. Thanks JTurner

  7. George Jones

    In future blog postings on “Irish Ancestry”, I hope that can more accurately let readers know upfront how they genetically (Autosomal) define and “estimate” “Irish Ancestry” in their DNA analysis and other narratives. See some of their web advertising below which I feel is misleading without additional caveats.

    Many people take their (and other DNA testing companies) “estimate” as a hard and fast and definitive admixture proportion …. it simply ain’t. It’s an inferred and estimated admixture proportion.

    The “Ireland Region” is one of 26 worldwide reference population groups they use. They specifically define the “Ireland Region” and “Irish Ancestry” in general as being made up of the Autosomal DNA from about 154 “Reference Natives” in Ireland – Wales – Scotland.

    So, Irish Ancestry is not just Ireland! Please make that clear.

    As an example, I am a Welsh Jones and there is NO stand alone Reference Population Group for Welsh. My Y-SNP is R1b-L371 and that is 100% in Wales … not Ireland. Plus, my Paternal Side Genealogical records go back to Wales in the 1600s. PLUS … “JONES” is a pure Welsh surname. The Welsh have pride to … just as the Irish do! shows me having an average 12% Irish Ancestry and they say their confidence in that single point stat is “not that high”. They list my Irish Ancestry range as 0% to 27% and they say they have more confidences in ranges than a single stat such as 12%. I only hope that they can get their hands on the POBI “People of the British Isles” Study and develop more refined reference population groups for Wales.

    Here’s what officially says in some sales like puffery:

    “The ONLY test that breaks out “IRISH ANCESTRY” from the larger UK, AncestryDNA can show you where your family likely came from, giving you a whole new way to connect with your cultural roots. You can even find family members you never knew you had.”

    Well there other 3rd party analysis tools at and other locations that can so some pretty nifty K-12 to K-20 analysis. One only has to download their raw DNA from to do this. So, there are OTHER ways at looking at Irish Ancestry and should cease the puffery and intimate they are the ONLY way for such analysis.


    • Julie Granka

      Hi George, thank you again for your comment. We encourage our customers to read through our ethnicity estimate help pages, as well as our Ethnicity Estimate White Paper, for a more detailed description of our methodology and approach. The AncestryDNA science team is working hard to further advance and refine AncestryDNA ethnicity estimation.

  8. George Jones

    Other lay Genetic Genealogists also see valid issues how DNA testing companies present and explain their biogeographical ancestry estimates overall and many times criticize a specific “ancestry estimate” be it Irish or otherwise.

    In 2014, a respected leader in our community said: “I’m certainly not saying that any company’s biogeographical estimates are perfect, or even correct. There is incredible room for improvement.”

    In 2012, this same respected leader in our community said: “Another issue with any biogeographical estimate is the labels used to describe a population. For example, what does “Scandinavian” or “Central European” really mean? Does “Scandinavian” mean that great-grandpa must have been a Swede, or does it mean something else? defines the “Scandinavian” with the modern day locations of Norway, Sweden, Denmark, but explains in their FAQ that it can mean much, much more”

    One of the big things that higher level Genetic Genealogists are looking for is an attitude for robust improvement and willingness to informally bring us into their fold via an “Irish American Advisory Board”, “African American Advisory Board”, “Welsh American Advisory Board”, etc. Another big thing would be to improve their reference panels by getting their hands on the POBI – People of the British Isles data.

    I will give credit where it is due and say that “overall” is doing a much better job than their competitors in this area of biogeographical ancestry estimates. This is thanks in part to the educational training, professional skills, and dedication of people at such as Julie Granka.

    Having said that, I realize that is on Version 2 of their ancestry estimates … I just hope that be fore Version 3 roles out they can seek out customer input by forming some of the Boards mentioned above.

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