Church Island (Welsh: Ynys Dysilio) 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 off the Belgian Promenade. The whole 2.7 acres (11,000 m2) of the island is taken up with St Tysilio's church, constructed in the 15th century, and the churchyard. The 20th-century bard Cynan (Albert Evans-Jones) is buried in the churchyard. The Anglesey Coastal Path passes the head of the causeway.
On top of the highest point of the small island is a memorial to the local men who died during the World wars. This is also the best place on the island from which to view the Menai Strait and the two bridges that cross it.
In 2002, Little Egrets bred in Wales for the first time on a small islet just off Church Island.