When did the first Irish immigrants arrive in the U.S.?
History of Irish Americans in Boston

The Port of Boston was a major center of immigration during the Great Irish Famine (1845–1852). By 1850, the Irish were the largest ethnic group in Boston. Most of the immigrants during this period were poor, unskilled laborers from rural backgrounds who settled in the slums of the North End, the South Cove, and Fort Hill. Many were not only destitute but weakened by typhus contracted on the coffin ships that had brought them. To contain the health risk, a quarantine hospital and almshouse were built on Deer Island, where hundreds of immigrants died and were buried in unmarked graves.[10] To make matters worse, a cholera epidemic swept through Boston in 1849. The North End poor, living in crowded, unsanitary conditions on the waterfront, were the hardest hit; over 500 Irish were killed.[11] Boston health inspectors described a typical Irish slum as "a perfect hive of human beings, without comforts and mostly without common necessaries; in many cases huddled together like brutes, without regard to age or sex or sense of decency."[12]