Find Ancestors

I am trying to find the irish origins of Patrick Mahon born in 1882. I am unsure if he was born in Ireland or in England. I know his parents were called Peter Mahon and his wifes maiden name was Kate Bush (from Rivelin is Sheffield). A relative of my nan did some research but unfortunatley he is now dead. All I know is that when he visited Ireland he found that alot of the family papers had been destroyed in a fire at 'a' registry office. Does anyone know anything about the above people or know how I can continue the search in to such a popular name?? Patrick married a Mary Jane O'Hara and they had numerous children, some died at birth or in infancy, Margaret, Alice and James are the ones I know about. My Nannan Lucy and her sister Ann are still alive but have as much info as me. After Mary's death, Patrick married a lady called Fogg who had children from another relationship.