Ruth Ferro 1890-1978

Looking to find where Einar J Ferro was born in Norway on 9th of november 1921? he died 24 october 1987 in the USA. Mother was Ruth Ferro, I was told that Ferro is the Americanized name, and that they came from a island outside Oslo that sounded like their lastname before it was Americanized so maybee a island with the name F.