Wexford takes its name from the principal town, Wexford, named 'Waesfjord' by the Vikings – meaning 'inlet (fjord) of the mud-flats' in the Old Norse language.

In pre-Norman times it was part of the Kingdom of Uí Cheinnselaig, with its capital at Ferns.

The County was formed in 1210 by King John during a visit to Ireland.

On Ptolemy's mid-2nd century 'Map' of Ireland Carnsore point appears as the Sacred Cape, the river Barrow as the Birgos (or Birgus), most of the area of County Wexford is shown as inhabited by a tribe called the Brigantes, and a tribe called the Coriondi (or Koriondoi) are shown as occupying north County Wexford

Early Irish tribes, forming the Kingdom of Uí Cheinnselaig included the Beanntraige, Uí Dego, Sil mBrain, Uí Bairrche, Fotharta Mara, and the Síl Maíluidir.

The county was one of the earliest areas of Ireland to be Christianized.