Looking for Mcdonald County Dublin Ireland

My great grandfather, Adam McDonald, was born in County Dublin, Ireland about 1836. He was in Placer County California by 1849, living in Iowa Hill and Forest Hill as a gold miner. He was married to Mary Bridget O'Donnell, who was also born in Ireland, about 1825. They had the following children: William, Alexander, (my grandfather), and Elizabeth. Adam died in May 1900 in Placer Co. CA.
I am looking for any information on parents or siblings in Ireland, also information on his date and place of arrival into the U.S.
Thanks