According to the Census, there are 34.5 million Americans who list their heritage as either primarily or partially Irish. That number is, incidentally, seven times larger than the population of Ireland itself (4.68 million). Irish is the second-most common ancestry among Americans, falling just behind German.
New York has the most concentrated Irish population; 12.9 percent of its residents claim Irish ancestry, which compares to a rate of 11.1 percent of the country overall. Boston, meanwhile, claims the most-concentrated Irish population for a city: 20.4 percent.
Trulia's chief economist Jed Kulko put all this data on a map, which shows the heaviest concentration of Irish-American zip codes. He notes that "Irish-Americans are at least 5 percent of the population in most counties across the U.S., and 10 percent or more in most of New England, New York state, New Jersey, eastern Pennsylvania, and other smaller counties across the country."
There is exactly one neighborhood in the entire country that has a majority-Irish population, according to the data Kolko looked at: Breezy Point in Queens. There, 54.3 percent of the population claims Irish ancestry. There are others though, that do get over 30 percent, as you can see in this map below.
"Eight of the top 10 metros where Ireland accounts for the highest share of foreign search traffic are also among the top 20 metros for the highest share of Irish ancestry," he writes. "In other words, people from Ireland tend to search more for homes in places where more Irish-Americans live."