Hor(ri)gan, Hanrahan, and Hourihane share similar heraldry but genetic evidence shows that they are distinct from each other.
Horrigan, Horgan, Hourihane, Horan, and Hanrahan often resemble each other in old records. Also mixed into this on occasion are Harrington, and Houlihan.
Peadar Ó hAnnracháin (1873 - 1965)
In his Southern Star column on January 18, 1947, this noted teacher, nationalist, writer, and editor of the Southern Star newspaper put his thoughts on Hourihane relationships in Cork to print:
It seems that there were three or four branches of the Hourihane or O'Hourihane clan in that area for those of the name who lived in the Clohane and Bauravilla district were not related to one another or to the Tooreen branch. Other branches lived in the Dunmanway district, and still another branch in Knockmore in the parish of Kilmacabea.
Note: Y-DNA testing has shown a distant, but recognizable relationship between Cloghane, Bauravilla, and Tooreen. This separation would be expected among descendants of men named Hourihane who have lived in the same general area for many hundreds of years.
On July 8, 1950, Peadar O'Hanrahan wrote of one historian's opinion on a Corca Laide origin:
..Diarmuid O'Mathuna... writes it O hodharadhain, and points out this was one of the clan names in Tuath O'hAnegusa, between Rosa and Dun Deide (Galley Head), whereas there as no such name as O hAmhrachain mentioned anywhere in the Geinealach of Corca Luidhe, as as the surname of Hourihan or O'Hourihane was pretty plentiful in Cairbre he claims his theory has much to reccommend it and susggests that it should be examined and studied.
The Celtic Society, in their publication of John Donovan's work, interpreted the original Irish as O'hOdhrain, and suggested it became Horan. See page 53 of the Miscellany.
Hourihane Howard
The South Irish Hourihanes (Howards) are actually closer in patriline kinship to men named Donovan and Collins than they are to Tipperary Hanrahans. Y-DNA testing has revealed a South Irish / Uí Fidhgeinte origin for these Hourihanes. Some of these may have also used the name Howard, sometimes at home in Ireland and often after they emigrated. Their paternal clan genetics are under R-CTS4466 > BY104765.
Hourihane Brien
Some Hourihanes using the name Brien appear to carry different Y patriline mutations than the Howards and they don't don't belong in the expected Y haplogroup of the Dalcassians. They fall somewhere under R-513. However the genetic data available so far to draw such a conclusion barely exists. More Hourihane Y-DNA data would be helpful.
Some west Cork Hourihanes used the modifier Glassogue, which might mean "stout." In Caheragh and Bantry area records it might appear like Glass or Glapogue. However, any genetic patriline correlation is unknown. Also unknown is whether there is a paternal clan relationship between the Fitzgerald Hourihanes of Ross to the Hourihanes of Castlehaven, Caheragh and Bantry.