With regard to the Irish-descended people in America, I think it’s safe to say that self-identification with the old country is a little more common than with any other old country, with the possible exception of Italy. Sad to say, the treatment of immigrants in America has not always been exemplary, and when the Irish began immigrating here in large numbers, in the 19th century, they were often disdained and marginalized by the Protestant mainstream. Italians were treated similarly. I think in the beginning, this fostered an “us/them” mentality on both sides, which may have led to a protracted tendency to self-identify as Irish within the group.
Staying in the cities of the East Coast after landing probably intensified this; they lived in poor areas of the cities, surrounded by other ethnic groups who didn’t like them (or each other), and fighting was a way of life for the boys of the neighborhood. In fact, according to Harpo Marx*, growing up Jewish in similar surroundings, there was a whole system of challenge and answer. If the Irish or Italian kids from the next block ganged up you, then, later, you’d round up some of your own guys and go over there and return the favor. Come to think of it, this labeling someone as being from the old country probably was protracted by the urban environment. In the same book, Harpo says that he quit school after the second grade, “for two main reasons–a big Irish kid, and a bigger Irish kid.” Those kids had probably been born in America, just as Harpo had, but given the endemic ethnic strife, the tendency to identify oneself, and others, with Old World cultures was strong.
It takes a long time to forget where you came from when you have to spend a few generations literally fighting for your life. Institutional discrimination and prejudice against Irish Americans belongs now to the distant past, but more subtle discrimination still exists. When JFK was nominated in 1960, many questioned whether a Catholic could get elected President in this country, and JFK is still the only Irish-American or Catholic president we’ve had. So the excesses and frivolity of Saint Patrick’s Day, and all the claims of Irish identity may well be rooted in the difficulties faced by the early immigrants. Any way you look at it, the experiences of the Irish in America shaped them and, IMO, fostered a cultural identity unique to them. It shaped them as much as the several Bloody Sundays shaped their cousins who stayed behind in the old country. Similar points could be made regarding Italian Americans.
So don’t judge these people too harshly for saying they’re Irish. They know they are Americans, but they’ve also got every right to take pride in their history, and the Irish ethnicity which defined them and, in the early years, was not watered down, but intensified by their struggle to succeed in a new country.