Genealogies have been compiled by people wanting to join a particular lineage society. Most people have heard of the Daughters of the American Revolution (DAR). This is a lineage society based upon service on the American side of the Revolutionary War. Societies typically see themselves as educators, historians and genealogists. They gather and preserve material for future generations to draw from.
There are hundreds of societies, each with different membership requirements. Yet, the common bond is genealogy. Membership is based upon an unbroken lineage from the applicant to an ancestor who meets the membership requirements. This has created a mountain of historical research, and a valid genealogical research tool for the rest of us. The Hereditary Society Community of the United States of America acts as an umbrella organization: – www.hereditary.us/about_hsc.htm Their website has links to the various societies.
The focus of a society can be immigration, time period, occupation, residence, religion or military service. Once you have determined how your ancestors fit historically in American history, then you can look for a lineage society which may have documented them.
Standards for lineage documentation have improved over the years. As with any genealogical material, lineage society papers are not always correct and must be tested for accuracy. The societies themselves monitor applications, often with a professional genealogist on their staff.
The papers for some lineage societies are on microfilm at the Family History Library. This makes research easy as you can study at the collections and applications for membership yourself.
Do not limit yourself to societies which may document an Irish immigrant. For example, if your Irish ancestor married a Norwegian, then you may want to look at any Norwegian societies to see if some mention is made about your Irish ancestor! Lineage society papers are an amazing resource.