Grandfather was a Luthern.
My great-great-grandfather (the cop) was descended from my patronymic ancestor, a Huguenot immigrant to Neiu Amsterdam, who was recorded in the Dutch census of 1645 dwelling in Neiu Utrecht (Brooklyn) and owning a goat and was a Dutch Reform minister on Staten Island by 1690.
But most of the later Irish immigrants were Catholic..so that would be the assumption I think ...
Was your grandfather Northern or southern Irish . the Northern Irish (protestants) were here early and fought in the revolutionary war