Seeking Donegan from Ireland to New York

My g-g-grandfather JOHN DONEGAN was b. in County Westmeath, Ireland, circa the 1830s. He emigrated to New York State, where he married MARY FARRELL, also of Westmeath, about 1850, probably in Haverstraw in Rockland County. By the 1860 census, John had died and his widow had married JOHN BANNON. All are most likely buried in St. Peter RC Cemetery in Haverstraw, but I can't find them in the cemetery records. Does anyone know any more about JOHN DONEGAN?