Looking for parents of Thomas McDonald (1843-1881)

My ancestor, Thomas McDonald, is said to have been born in Bandon on July 20, 1843. He came to the US when about 4 years old with his parents who may have been Thomas McDonald and his wife, Mary. Her maiden name might have been Carthy. He may have had a younger brother, Patrick.  I would like to know more information on this family such as to verify his parents, if he had a brother, Patrick, his mother's maiden name, and if there were other family members who stayed in the Bandon area who might have descendants there now.

I believe Thomas McDonald, the father, was a stone mason, a trade he would have learned in Bandon. After a year on the east coast of the US, he relocated in about 1848 to La Salle, Illinois, with his wife and young Thomas to work on the building of the stone works of the Illinois Canal.  I believe he died a few years later.  His son, Thomas, joined the Union Army in 1862 at age 18 during the Civil War and rose quickly to a  Sergeant-Major in the Quartermaster Corps of the 90th Illinois Volunteer Infantry. He served throughout the war and then became a detective with the famous Pinkerton Detective Agency in East Coast cities.  In 1867, he married Mary Theresa Corley, daughter of Martin Corley, who had emigrated from Parish Ahascragh in Galway.  

Thomas and his wife then settled in Iowa to farm, he was elected twice to be county treasurer of Shelby County, Iowa, founded a town in that county called Corley, Iowa, named after his wife, and secured land and organized the construction of a 13 mile railroad spur to his town.  For this effort, he was named President of the Avoca, Harlan and Northern Railroad which had stop in Corley, Iowa.  At the time of his death in 1881 at only age 38, he had a farm of 600 acres and he and his wife had five children, one of whom was my grandfather.

Any help with the information on family of Thomas and Mary McDonald would be appreciated.