What Do Boston, Philadelphia, and Pittsburgh Have in Common?
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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 1600s and 1700s, 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. Irish_city_map 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.