The Irish Civil Registration Indexes for have now gone online on the Family Search pilot site. The indexes include births from 1864 to 1958, marriages from 1845 to 1958 and deaths from 1864 to 1958. I've done a quick search to establish the distribution of the variant spellings in the Irish records. The total number of birth, marriage and death events for each spelling are as follows:
It does not seem to be possible at present to search separately for births, marriages and deaths. The four Cruwyses in the Irish indexes are all in my own family tree. I have not yet had the chance to explore any of the other Irish lines.
The surname in Ireland, as in England, has a very long history. It seems likely that the name arrived in Ireland following the Anglo-Norman invasion in 1169. The earliest reference to the surname I have found in the Irish records relates to a Philippum de Cruce of Dublin who is mentioned in the Patent Rolls in 1229. A Miles de Cruys is noted as holding lands in the manor of Balimaglassan in County Meath in the Patent Rolls in 1277 and 1279. Cruys seems to have been the predominant spelling in the medieval period, whereas today the Cruise spelling is the one most commonly found in Ireland. The family has given its name to a small parish in County Meath which is known as Cruisetown. Another branch seems to have settled in Dublin. The chief seat of the family was at Naul, and the ruins of their castle can apparently still be seen today.
In order to keep the one-name study to a manageable size I have deliberately excluded the variant spelling Cruise because of the numbers involved both in Ireland and America. I do however have some Cruises in the DNA project, and I have acquired a few Irish records in the last few years so I am always pleased to hear from anyone researching the surname Cruise. My hope is that one day someone might be interested in taking on Cruise as a separate one-name study!