3/17/17 St. Patrick’s Day is March 17, when about 39 percent of Americans say they celebrate their Irish heritage. More than 4.5 million Irish immigrants arrived in the U.S. between 1820 and 1930. Between 1820 and 1860, the Irish constituted more than one-third of all immigrants to the U.S. Here is a look at many waves of immigrants coming to America over the decades. Report