Anglesey ( ANG-gəl-see; Welsh: Ynys Môn [ˈənɨs ˈmoːn]) 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 (Ynys Gybi) 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 Isle of Anglesey has an area of 275 square miles (712 km) and had a population of 69,097 in 2024. After Holyhead, located on Holy Island, the largest settlements are Llangefni in the centre of Anglesey and Amlwch on the northern coast. The economy of the county is mostly based on agriculture, energy, and tourism, the latter especially on the coast. Holyhead is also a major ferry port for Dublin, Ireland. The county has the second-highest percentage of Welsh speakers in Wales, at 57.2%, and is considered a heartland of the language. The Isle of Anglesey is part of the preserved county of Gwynedd.