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Number of de Courcy households by County
during Griffiths Valuation 1847-64
Cork 4 Kerry 3
Limerick city 1 Waterford 1
Number of de Courcey households by County
during Griffiths Valuation 1847-64 Clare 1 Cork 18
Dublin 2 Galway 4
Mayo 1 Waterford 4
Surname Variants Total
De Courcey 5
De Courcy 9
De Coursey 2 Total 55
How common is the surname?
This table shows how relatively rare the de Courcy surname was by county during the 1848-1864 Griffiths Valuation. If the surname is very rare, then you can be more certain that a name which matches your ancestor's is more likely to be the correct person. If the name is common, then you may need more details to verify the match. This information is available for most Irish surnames at the Irish Times web site.
4. 1911 Census transcription errors: there are several "de Courcy" transcription errors in the on-line census data from the National Archives of Ireland. All of the de Courcys in Waterford and some others are erroneously transcribed as "De Courey" or Decourey", and Dunmore East is erroneously transcribed as "Durunore Town". However, the original handwritten returns are correct. The errors were reported to the National Archives in 2009, but as of May 2010 they had not yet been corrected. So, if you cannot find the expected names, you could try searching for the above mis-spellings.
Y-DNA Test Results
A Y-DNA project for all spelling variants of the de Courcy name is posted at "The "Coursey/DeCoursey" Group Project". The project results include three distinct haplogroups (I1d1, R1b and J2), indicating widely different ancestral origins. However, the probable haplotype of John de Courcy (1160-1219) is not yet known.
A descendant of Dominick de Courcy (1720-1776) submitted a Y-DNA37 test in September 2010. The results (C-17) are posted at Y-DNA results and are unusual in that there is only one match at the 12 marker level and no matches at 25 or 37 markers in the whole database. Due to the unusual haplotype, a backbone test was performed, which confirmed the haplogroup is R1b1b2 (R-M269 SNP tested positive), consistent with the Celtic/Basque (Atlantic) Modal Haplotype.
What can be inferred from these Y-DNA results?
As a result of their conquests, High Kings, War Lords, and Knights of old, such as "John de Courcy, 1160-1219" (JdC) typically fathered numerous offspring, which could be expected to lead to a large number of direct descendants alive today (e.g. compare King Niall). Hence, a significant number of very close matches in the de Courcy Y-DNA database might be circumstantial evidence that the group was decended from JdC. There is one large group (I1d1) and two smaller groups (J2a4 & R1b1a2) in the de Courcy Y-DNA database.
However, as the Waterford (Dominick) de Courcy family haplotype is so rare and does not closely match any of the other results, it could be inferred that they are probably not descended from JdC.
If we assume that the Waterford de Courcy's are not descended from JdC, then one explanation is that the name was adopted by a close associate of JdC or his descendant (e.g. faithful knight or servant), as was common when surnames first started to appear. This is not inconsistent with the fact that the Waterford de Courcys have long been honoured as Freemen of the City of Waterford. Alternatively, it is also possible that there was an adoption or other event that interrupted the male lineage (Y-DNA) in this particular line.