I'm sure other people know a lot more than I, but my take would be that the only two recent powerful Irish American criminal organizations in recent memory were the Westies and Winter Hill Gang.

Hell's Kitchen has about as many ne'er-do-well native Irish youths running around it these days as it does gorillas. Any potential Westie left would make about 10 times more selling his mom's flat than he would in 10 years of criminal activity.

South Boston has become fairly gentrified too, and far less homogenous Irish. There are probably a few very loosely organized guys still running around but I doubt anything you could really call a mob/mafia.

Irish by and large were mid- 19th century immigrants to the US, while Italians were more early 20th.