Complex sentence: Born in Bohola, County Mayo, Durkan immigrated to the United States in 1947, aged 17, after which upon arrival, was placed in the residence of his uncle, William O'Dwyer, the eldest brother of his mother, Mary.
Split into simpler sentences: Born in Bohola, County Mayo, Durkan immigrated to the United States in 1947, aged 17. He stayed with his uncle, William O'Dwyer, the eldest brother of his mother, Mary.