Italians settled together in America, so if you can't find your ancestors' homeland, study his neighbors.
Italian newcomers clustered in America with their paesani (fellow villagers). If you can't find the place in Italy where your ancestors originated, check out the neighbors. For example, immigrants from Lombardy and Sicily settled a part of St. Louis that become known as "Dago Hill." In New York City, Neapolitans occupied the Mulberry Bend neighborhood; Baxter Street near Five Points drew Genoese; Houston and Spring streets housed Sicilians; and East Harlem's 112th Street attracted villagers from Avigliano. Most residents of Pittsburgh's Panther Hollow district were from Abruzzi. Sicilians from four villages — Santo Stefano Quisquina, Alessandria della Rocca, Cianciana and Contessa Entellina — populated a community in Tampa, Fla.
Italians displaced 19th-century Irish immigrants in urban ghettos — the largest of which were in New York City, Boston, San Francisco and New Orleans. But like other ethnic groups, as Italians became financially able, they moved out of big cities. In fact, new immigrants' mobility may cause you problems locating them in census records — they often changed residences three or four times during their first few years in the United States.
Italian character also may explain an absence from censuses. Because of their emphasis on family loyalty, southern Italians tended to distrust outsiders, especially government representatives such as census takers. Since some Italian immigrants viewed education as a threat to family unity and economy, their children had high truancy and dropout rates, so school records may be helpful. Call school districts in your ancestors' area to ask where records are archived.