Irish ancestry refers to blood relatives in your past who were of Irish descent. Dictionary.com defines ancestry as the lineage or descent of a family.
According to the U.S. Census Bureau, 36.2 million Americans claimed Irish ancestry in 2008. In the U.S., Irish ancestry can be traced back through the 17th century. By the time of the Revolutionary War, a half million Irish people had immigrated to the United States. In the 19th century, emigration from Ireland increased due to the need for labor to meet the demand for developing large infrastructure projects. With industrialism, many Irishmen left farm labor to work in factories and on railroads. Additionally, immigration to the U.S. increased with the Great Irish Famine that swept Ireland in the 1840s. Concentrations of Irish are found all over the country, but especially in New England, New Jersey, Pennsylvania and New York.