My Porterfield ancestors only stayed in Ireland for about one generation before moving on to America (see below information). I have not been able to connect my ancestors to those Porterfields who came to America from Ireland at a later time, although I am sure they are connected to the same Porterfields from Scotland. More than likely, your ancestor was also "young William Porterfield" discussed below, or at least from the same family. Do you have a copy of Frank Burke Porterfield's 1947 book, The Porterfields? It contains a lot of history of the Porterfield family in Scotland, migration to Ireland, then on to America.
Here is a sample of what I have collected. You are undoubtably connected to these same Porterfields from Scotland.
Late in the seventeenth century, young William Porterfield left Kilmacolm, Scotland for Ireland. His older brother, Alexander, had inherited the family estate of Duchal when his grandfather John died. A generation later, William's son John left County Donegal, Ireland, with his wife and family for America. The Porterfield family had a long and colorful history in the area known as Renfrewshire, which is just west of Glasgow. This information is mainly taken from a small book by Elizabeth Main, A Kirk Without a Steeple, Being a History of the Old Kirk and Parish of Kilmacolm.