A compilation of facts and statistics (with direct links to sources) from the U.S. Census.
From the Compilation:
Congress designated March as Irish-American Heritage Month in 1991 and the president issues a proclamation commemorating the occasion each year.
Originally a religious holiday to honor St. Patrick, who introduced Christianity to Ireland in the 5th century, St. Patrick’s Day has evolved into a celebration of all things Irish. The world’s first St. Patrick’s Day parade occurred on March 17, 1762, in New York City, featuring Irish soldiers who served in the English military. This parade became an annual event, with President Truman attending in 1948.
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