This source puts that number at 35M of people with "some" Irish descent: https://overlandirelandtours.com/blog/why-are-there-more-iri... — that means that most of them probably have some other heritage too.

People say similar stuff about Serbians in Chicago (how it's the second biggest Serbian city after Belgrade), but usually all of that is overestimated significantly. Just like people overestimate their local city population (most in Belgrade claim it has 2M people when census on a metropolitan area gets us to 1.57M).

People say a very similar thing about the number of Greeks in Melbourne, Australia.