According to the wikipedia page about Italian emigration (in Portuguese, but the table with immigrants to each country is very easy to read) the U.S. received 5.6 million Italians between 1870 and 1970, Argentina received 2.9 million and Brazil received 1.5 million.
Italian Brazilians are the largest number of people with full or partial Italian ancestry outside of Italy, with São Paulo being the most populous city with Italian ancestry in the world. Nowadays, it's possible to find millions of descendants of Italians, from the southeastern state of Minas Gerais to the southernmost state of Rio Grande do Sul, with the majority living in the São Paulo state and the highest percentage in the southeastern state of Espírito Santo (60-75%). Small southern Brazilian towns, such as Nova Veneza, have as much as 95% of their population of Italian descent.
From the same wikipedia page in Italian, the number of descendants (also easy to read table):
Brasile = 27 200 000
Argentina = 19 700 000
Stati Uniti" = 17 250 000
The page about American Italians (in English) confirms 5.5 million Italian immigrants to the U.S.