Church Island, also known as Llandysilio Island,^[1] (Welsh: Ynys Tysilio) is a small island in the Menai Strait on the shores of Anglesey to which it is attached by a short causeway that is reachable only on foot. The dominant feature of the island is with St Tysilio's Church, constructed in the 15th century, its churchyard, and a grade-II listed war memorial. The 20th-century bard Cynan (Albert Evans-Jones) is among several notable people buried in the churchyard. The Anglesey Coastal Path passes the head of the causeway.

A number of birds inhabit the island and its waters, and it also features numerous primroses.

Church Island is located in the Menai Strait, off the south-eastern shore of the island of Anglesey, close to the town of Menai Bridge.^[2] It is located in a stretch of the Menai known as the Swellies, with the stretch of water to the south of the church is prone to dangerous tidal currents.^[1] Access to the island is via a short tidal causeway, which meets the Wales Coast Path long-distance footpath at its Anglesey end. The closest road is the A545,^[2] with a car park from which the island can be accessed via a woodland path.^[1]

St Tysilio's, a single-chamber church, is the major feature on the island,^[1] along with its graveyard and a war memorial near the highest point, which was designed by Harold Hughes and was given a grade-II listing in 1997.^[3]

The early history of the island, including details of the construction of the causeway to the Anglesey mainland, is unknown.^[4] The first recorded occupation was by Prince Tysilio, later Saint Tysilio, who was the son of Brochwel Ysgithrog, a king of Powys. Tysilio arrived on Church Island in approximately AD 630, and founded a hermitage there. He remained there for around seven years, before moving to Meifod where he became an abbot.^[5] No trace of Tysilio's hermitage survives on Church Island today.^[5]

The present-day church of Saint Tysilio was founded in the fifteenth century.^[6] It is not known who built the church, but it is likely that it replaced an earlier structure on the same site.^[4] Several prominent people are buried in the churchyard, including Henry Rees Davies,^[6] other members of his family such as father Richard Davies,^[4] John Edward Lloyd, and the bard Albert Evans-Jones, known by the pseudonym of Cynan.^[6]

Birds found close to the island include oystercatchers, curlews, common terns, and in recent times, little egrets. There are also a number of primroses growing, which give the island a golden appearance during the spring months.^[1]

• Ynys Gored Goch