Interesting no? When most people discuss Irish-Americans they are usually talking about the "famine Irish" who came in the 1840's but the first wave of Irishmen to arrive to the "Colonies" tended to come from Ulster.
Driven in a great part by religious persecution caused by the Test Act which drove the "dissenters" (they are called Presbyterians in America) out of Ireland.

By the time of the American Revolution it is estimated that close to 250,000 Irish had arrived in America.