There are many Welsh surnames which are common to all of Wales or of more localised distribution.
Ellis is a surname found in pockets of North Wales particularly in Flintshire, Caernofonshire, Meirionethshire and north Montgomeryshire. Elsewhere it is not so common.
Evans, a patronymic surname is derived from the Welsh for John Ieuan, which in turn is from the Latin Johannes. It is found all pver Wales.
Griffiths is also a patronymic surname from the Old Welsh Grippiud which became Gruffydd or Griffiths. This name is found distributed through Wales with high concentrations on the Llyn Penninsular.
Gronow derives from the personal name Gronwy. This name is more heavily concentrated along the border are of the Marches and is also found in Shropshire.
The most common Welsh name is Jones or sometime Jone ( mainly in Gower). It is a patronymic surname derived from the personal name John. It is most heavily concentrated in North Wales