Llanddeiniolen is a community in the county of Gwynedd, Wales, and is 124 miles from Cardiff and 206 miles from London. It comprises the hamlet also called Llanddeiniolen, and the villages of Deiniolen, Bethel, Dinorwig, Rhiwlas, Brynrefail and Penisarwaun. It is the third-largest community by population in Gwynedd, with 5072 people in the 2011 census. Also in the community is the dispersed settlement of Fachwen, located on the north shore of Llyn Padarn.