There is a website called Ireland Reaching Out which might be helpful. They have a message board where you can ask questions and people who are willing to locate sources for you. They will probably be able to give you a few ideas on pinnning down the area of origin. Also, if you browse through some Irish genealogy resources, you might be able to pin down his origins more specifically. Some surnames are found in particular areas eg. Terry (Therry) is found in Cork and Waterford. A death record may be helpful as sometimes this states the County of origin (this is common in Australia). Irish records are tricky as the church held early records and these are parish based and few are indexed. Military records are probably worth a look.