This website has an interesting tool where you can type in a certain city or neighborhood of that city and can see the demographics of that area. You can see the demographics of specific countries (Irish,Polish,Italian,Greek,ect).
Some places that were insteresting-
South Philly have places as high as 85% percent of Italians
Morris Park in the Bronx still has areas over 60% Italian
Woodlawn Bronx and Canaryville Chicago of course have a high percentage of Irish
Bensonhurst still has areas well over 50% Italian.
And nonose, not trying to call you out but the demographics for Bridgeport says 20-40% Italian.
Here is the website http://www.city-data.com/