The Old Church of St Gwenllwyfo, Llanwenllwyfo is a medieval ruined church near Dulas, in Anglesey, Wales, perhaps built in the 15th century to replace another church from which only the 12th-century font survived. Dedicated to Gwenllwyfo, a 7th-century female saint about whom nothing else is known, it was used as a chapel of ease for the church in Amlwch, about 5 miles (8 km) away. Restored in 1610 and again in the 18th and 19th centuries, it contained an oak screen and pulpit from 1610.

St Gwenllwyfo's Church is a 19th-century parish church near the village of Dulas, in Anglesey, Wales. It was built between 1854 and 1856 to replace an earlier church in the parish, also dedicated to St Gwenllwyfo, which needed repair and had become too small for its congregation. The new church was built nearer to the Llys Dulas estate, whose owner contributed £936 towards the total cost of £1,417, rather than near the area where many of the parishioners lived. In 1876, Sir Arundell Neave donated 27 panels of 15th and 16th-century stained glass that had once belonged to a Flemish monastery.