It derives not from Irish but from Old Norse, most likely either Vikingalo, meaning 'meadow of the Vikings', or Vik-lo, 'meadow of the bay'. That Scandinavian root points to a settlement here long before the Normans arrived, and the granting of Wicklow castle to Strongbow by Henry II in 1173 seems to confirm it: you do not grant what does not already exist in some form.

By the mid-thirteenth century the town had taken on enough shape that a 'King's street' appears by name in a deed dated to 1256 to 1268, a detail that suggests a degree of civic organisation. The town was captured in 1301 and fell into a period of decline, though it recovered to prominence again in the late sixteenth and seventeenth centuries. That recovery came with some anxiety about defence: in 1576, earthwork ramparts were thrown up around both Wicklow and Arklow, the kind of improvised fortification that speaks to an unsettled political landscape rather than confident expansion. Wicklow also accumulated an unusual density of religious institutions for a town of its size. Alongside the Franciscan Friary, a Benedictine convent existed here between 1448 and 1470, and as late as 1578 there was a functioning leper hospital, the presence of which hints at a community still organised around medieval patterns of charity and spiritual obligation even as the wider world was shifting around it.