I don't think this will help you much, but my grandfather, Joseph Lusk, was born in Banbridge, County Down, (Northern) Ireland in 1858, and came to Mass. in 1888. He had several sisters, but no brothers. His parents were John and Rachel (Corry) Lusk. My mother told me years ago that her father had a cousin named John, who also came over from Ireland, and was thought to have moved out west from New York. Although I don't know the names of earlier generations of my grandfather's cousin, I believe my great grandfather John, who was born in 1822, was the son of George and Isabella Lusk, who lived in Dromore Parish, County Down. It would appear that my grandfather's cousin John was named after his uncle, my great grandfather. Could your William have been my great grandfather's brother?