Italian ancestry is the fourth largest European ethnic group in the United States. About 5.5 million Italians immigrated to the United States from 1820 to 2004. Italian immigration began in earnest during the 1870s, when more than twice as many Italians immigrated than during the five previous decades combined.

Italian navigators and explorers played a key role in the discovery, exploration and settlement of the Americas. Christopher Columbus, the explorer who first reached the Americas in 1492–1504, was Italian.

Another notable Italian explorer, Amerigo Vespucci, who explored the east coast of South America between 1499 and 1502, is the source of the name America.

England's claims in North America were based on the voyages of the Italian explorer John Cabot (Giovanni Caboto) and his son Sebastian Cabot (Sebastiano Caboto) in the early 16th century. In 1524 the Italian explorer Giovanni da Verrazzano was the first European to map the Atlantic coast of today's United States, and to enter New York Bay.

A number of Italian navigators and explorers in the employ of Spain and France were involved in exploring and mapping their territories, and in establishing settlements; but this did not lead to the permanent presence of Italians in America.

In 1539, Marco da Nizza, explored the territory that later became the states of Arizona and New Mexico. In the 17th century, Henri de Tonti (Enrico de Tonti), together with the French explorer LaSalle, explored the Great Lakes region.

De Tonti founded the first European settlement in Illinois in 1679, and in Arkansas in 1683. With LaSalle, he co-founded New Orleans, and was governor of the Louisiana Territory for the next 20 years. His brother Alphonse de Tonty (Alfonso de Tonti), with French explorer Antoine Cadillac, was the co-founder of Detroit in 1701, and was its acting colonial governor for 12 years.

Spain and France were Catholic countries and sent many missionaries to convert the native population. Included among these missionaries were numerous Italians. Father François-Joseph Bressani (Francesco Giuseppe Bressani) labored among the Algonquin and Huron Indians in the early 17th century. Between 1687 and 1711, the southwest and California were explored and mapped by an Italian Jesuit priest Eusebio Kino (Chino).

The first Italian to reside in America was Pietro Cesare Alberti,[19] a Venetian seaman who, in 1635, settled in what would eventually become New York City. A group of around 200 Waldensians arrived from Northern Italy in 1640 in search of a more hospitable place to practice their Christian faith.

The Taliaferro family, originally from Venice, were one of the first families to settle in Virginia, while the Fonda family settled in present-day upstate New York, establishing the town of Fonda.

Francesco Maria de Reggio, an Italian nobleman who served under the French, came to Louisiana in 1751 where he held the title of Captain General of Louisiana until 1763. Today, the descendants of the Alberti/Burtis, Taliaferro, Fonda, Reggio and other early families are found all across the United States.

The 1870s were followed by the greatest surge of immigration, which occurred in the period between 1880 and 1914 and brought more than 4 million Italians to America. This period of large scale immigration ended abruptly with the onset of the First World War in 1914 and, except for one year (1922), never resumed. Further immigration was greatly limited by a number of restrictive laws passed by Congress in the 1920s.

Approximately 84% of the Italian immigrants came from Southern Italy and Sicily. These were largely impoverished agricultural and overpopulated regions. The Italian government initially encouraged emigration to relieve economic pressures in the South.

After the American Civil War, which resulted in over a half million casualties, immigrant workers were recruited from Italy and elsewhere to fill the labor shortages in the United States caused by the war. Most immigrant Italians began their new lives as manual laborers in Eastern cities, mining camps, and in agriculture.

Italian Americans gradually moved from the lower rungs of the economic scale to a level comparable to the national average by 1970. By 1990, more than 65% of Italian Americans were employed as managerial, professional, or white-collar workers.

The Italian-American communities have often been characterized by strong ties with family, the Catholic Church, fraternal organizations and political parties.

Today, over 17 million Americans claim Italian ancestry. There is an Italian population in all 50 states, with the highest concentrations in New York, California, New Jersey, Pennsylvania, and Florida. Seven states have a population of over 10% Italian:

• 1.Rhode Island 18.9%
• 2.Connecticut 18.7%
• 3.New Jersey 16.8%
• 4.Massachusetts 13.9%
• 5.New York 13.5%
• 6.Pennsylvania 12.2%
• 7.New Hampshire 10.7%