The evidence for this English place-name could be understood to support straightforward derivation from a compound of ‘Orris’ as suggested by O’Donovan (13) + -town, or perhaps Orr + (ə)s + -town, with a vowel before the genitive marker -s (as found in South Wexford and elsewhere in the Pale; see CODDSTOWN (#54405), par. Ballymore).

However, it is striking that the earliest form ‘Overstowne’ (1) is also found in the early evidence for the similarly named Oristown in Meath. The oldest historical references to that townland, dating from the sixteenth century, are ‘Overston’ and ‘Overestone’ (see logainm.ie). It would appear, then, that the first element in both place-names ultimately derives from the Anglo-Norman surname Over or Overy (see Reaney, 1970 p.238). [Note that this name is attested in Wexford in the fourteenth century, e.g. 1399 ‘Rich. Overy, of Templetown’ (Hore iv p.282). This loss of -v- reflects an attested linguistic development — internal -v- was certainly sometimes lost in the dialect of English spoken in south Wexford (see The Dialect of Forth and Bargy, County Wexford, Ireland viz. Lerock < ME Laverock)]

The Meath townland is attested in Irish sources as ‘baile Oirthidhean’, ‘do bhaile Óirthidian’ and ‘Baile Órtha’ (see FSÁG Baile Oirthidhean); the form recorded from local Irish speakers in 1836 was ‘Baile Órthaidhe’, which has been standardised to Baile Órthaí (see logainm.ie; see also Joyce ii p.451). In light of the apparently identical development of both names in English, the same Irish form is suggested for Orristown here.

[Since publication of this note an earlier historical form of this place-name has been found, namely ‘Orreistowne’, which is in line with all historical forms of this place-name other than ‘Overstowne’, possibly reflecting a surname other than Overy such as ‘Oure’ which is also attested among the Anglo-Normans in Ireland (see Calendar of Documents, Ireland 1293‒1301 numb. 47, 89, 391: note also ‘Nicholas de Ouer’, Calendar of Documents, Ireland 1293‒1301 p.292). The Anglo-Norman surname ‘Oure’ could certainly generate the initial element of Orristown. However, the historically attested form ‘Overtowne’ does not bear the usual characterics of a scribal error, which normally consist of a misread consonant, or a variant spelling where replacement of one vowel with another is common as in the late historical form ‘Arastown’. Therefore, it is perhaps best to apply the principal of lectio difficilior potior “the more difficult reading is the stronger” in the case of ‘Overstowne’, and understand it to indeed reflect the original nature of this place-name. In any case, the evidence for this place-name clearly suggests English (Anglo-Norman) origin, as is the norm for place-names in this area.]

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