Deiniolen is a village in Gwynedd, Wales, at the foot of Elidir Fawr, in Llanddeiniolen Community. Deiniolen has views over Caernarfon and on a clear day, Holyhead Mountain and occasionally the Wicklow Mountains in Ireland, can be seen. The population of the electoral ward was 1,909 as of 2011, including nearby Dinorwig, with 81.2% of the population speaking Welsh. The community, Llanddeiniolen, has a population of 5,072 as of the 2011 census, the third-largest in Gwynedd.

Gwynedd is a county in the north-west of Wales. It borders Anglesey across the Menai Strait to the north, Conwy, Denbighshire, and Powys to the east, Ceredigion over the Dyfi estuary to the south, and the Irish Sea to the west. The city of Bangor is the largest settlement, and the administrative centre is Caernarfon. The preserved county of Gwynedd, which is used for ceremonial purposes, includes the Isle of Anglesey.