St Cristiolus's Church, Llangristiolus is a medieval church near the village of Llangristiolus, in Anglesey, north Wales. The village, about 1 mile (1.6 km) from the building, takes its name from the church. Reputedly founded by St Cristiolus in 610, the present building dates from the 12th and 13th centuries. Alterations were made in the 16th century, when the large east window in Perpendicular style was added to the chancel – a window which has been described by one guide to the buildings of north Wales as "almost too big to fit" in the wall.