The small parish of Deneio comprises the borough of Pwllheli and higher arable land to the N., together with land reclaimed from the sea by the construction of embankments on either side of the harbour under an Act of 1811. At the time of the Edwardian conquest the borough had twenty burgages, held on such a tenure as to suggest that borough and market had been created by one of the welsh princes on the Anglo-Norman model, but the town plan does not indicate any formal and regular layout, and the earliest surviving buildings are of the 17th century.
A full discussion of the former topography and early settlement, by Professor T. Jones-Pierce, is given in Trans. Caerns. Hist. Soc., III (1941), pp. 9-32.