Over four million Irish immigrants came to the United States between 1820 and 1930. With or without the O, according to a tally of surnames in the 2000 US census, these are nine of the most common Irish surnames in America. Subscribe to IrishCentralWhile you can explore the roots of your own Irish surname with on Ancestry, here is a breakdown of some of the most popular Irish surnames in the US:Murphy10At the end of the 19th century, Murphy was the most prevalent surname in Ireland and was particularly associated with Counties Cork and Wexford. So it’s not surprising that it’s now the most common Irish surname in the United States. Unusually for Irish names, the “O” prefix has held strong, with more O’Connors than Connors in both Ireland and America.