I ran across this page whilst doing some Lancashire research: http://www.thelancashireresearcher.co.uk/irish.htm -- > My great grandfather Dominic Costello arrived in the Lancashire town > of Bury around 1865 and is one of my four Irish born great grandparents. > > Despite the usual problem for those of us with Irish ancestors in > having very little information on the geographical origin of our > forebears, I succeeded in finding the birthplace of Dominic with a lot > of patience and determination, several trips to Ireland and a little > luck. The full story of my research entitled 'The Clan Costello' was > published in M&LFHS journal Vol 33 1997 {now out of stock}. The > article won the Earwaker Prize for the best article published in the > journal in the12 month period of 1997. > > For Irish family research it is necessary in most cases to have at > least the county of birth. In my case I was lucky that the name > Costello was one of the hereditary surnames of Ireland: It came into > being around the eleventh century. At first the surname was formed by > prefixing Mac to the father's name or O to that of the grandfather or > earlier ancestor. > > {Mac} Costello{e} MacOisdealbhaigh. Oisdealbgh was the name of the > father of Gilbert de Nangle, and this is the first example of a Norman > family assuming a Mac name. The use of the prefix O is erroneous , > though it does occasionally occur in seventeenth century records. The > barony of Costello is in east Mayo. See Ed MacLysaght , 'The Surnames > of Ireland' > > My great grandfather Dominic Costello was born in the townland of > Ballyglass, parish of Kilmovee, Co. Mayo. The parish is East Co. Mayo > near the border of Roscommon. I have second cousins still living in > Kilmovee. There is evidence proving that the Costellos were living in > Ballyglass since 1464. Hope this helps someone. Best wishes, Lynne