This place-name does not appear to be of Irish origin and may in fact be one of the few toponyms in Wexford derived from Norse.

Superficially, Arklow resembles an anglicisation of ‘Árd-chloch’ [Ardchloch] or similar, as proposed by O’Donovan (9) (cf. BPP p.16). However, none of the anglicised examples of the name show any trace of final -ch. The absence of any unambiguous reflex of the dental -d- of this proposed Irish form is also problematic. The historical evidence for other place-names shows that where there was a loss of an interconsonantal dental, the early anglicised forms show a clear reflex of the dental while later anglicisations contain a compensatory vowel in the position of the original dental, e.g. Arragurteen < Ardgurtin < Ardghoirtín (see ARRAGORTEEN (#52772), par. Killenagh). As the evidence for Arklow displays none of these characteristics, and given that no other plausible Irish precursor presents itself, it seems best to consider the name to be of non-Irish origin.

By contrast, the similarity to Arklow (#1416540) in Wicklow is of course conspicuous and the likelihood of a shared origin is very strong, as pointed out by Colfer (2002 p.22; cf. BPP p.16). One possible derivation might be the Norse personal name Arnkell compounded with ló “swamp” or “low-lying meadow near water” (see Price, 1967 p.477: cf. ‘ló ON “a glade, a meadow”’, EPE ii p.25; see also Etchingham, 1994 p.124; Mac Giolla Easpaig, 2002 p.466). Note that the minor name Selskar Rock near the mouth of Bannow Bay, only six kilometres from this townland, confirms a one-time Norse presence in this general area (see SELSKAR, par. (#2625)).

[Excerpt from Logainmneacha na hÉireann IV: Townland Names of County Wexford, 2016]