Holy Island is an island on the western side of the larger Isle of Anglesey, Wales, from which it is separated by the Cymyran Strait. It is called "Holy" because of the high concentration of standing stones, burial chambers, and other religious sites on the small island. The alternative English name of the island is Holyhead Island. According to the 2011 UK Census, the population was 13,659, of whom 11,431 (84%) lived in the largest town, Holyhead.

Anglesey is an island off the north-west coast of Wales. It forms the bulk of the county known as the Isle of Anglesey, which also includes Holy Island and some islets and skerries. The county borders Gwynedd across the Menai Strait to the southeast, and is otherwise surrounded by the Irish Sea. Holyhead is the largest town, and the administrative centre is Llangefni. The county is part of the preserved county of Gwynedd.