The county of Anglesey (Ynys Mon) is an island off the north-west coast of Wales and is also known as the Isle of Anglesey. It includes Holy Island across the narrow Cymyran Strait on the north-west tip of Anglesey. Anglesey island, at 260 square miles, is the largest island in Wales and is separated from the mainland by the Menai Strait, spanned by the Menai Suspension Bridge which was designed by Thomas Telford in 1826. The Menai Strait is also spanned by the Britannia Bridge, built in 1850 and replaced in 1980. The largest town is Holyhead on Holy Island.

There are numerous megalithic monuments and menhirs on Anglesey, testifying to the presence of humans in prehistory. Plas Newydd is near one of 28 cromlechs that remain on uplands overlooking the sea.