David, As close as I can figure from US Census records, Mathew O'Brien was born about 1802, perhaps Julia was a sister or cousin. I don't have any information on him other than name and that his sister's name was Mary. His sister Mary married a John Carty (Carthy) I am not sure if that was in Ireland or USA. He had a daughter named Mary Jane and she was supposedly born in Co. Meath Ireland but raised in a convent as her mother died when she was young, Mathew never remarried and Mary Jane was on the 1850 census with her father Mathew in Missouri, also listed with them were Mary Trainor and Philip Trainor. Does any of this sound familiar to you? Sorry it has taken me so long to reply.