Throughout its history the village has had three names. The first was Castell Iorwerth ("Iorwerth's Castle") after an important Welsh prince of the time. The second name, Cemais, is similar to the modern name and refers to the meanders in the River Wygyr that are near the village. The name of the nearby Wylfa nuclear power station is linked to the village. The late 19th-century Cemaes resident David Hughes, who travelled to Liverpool and found riches in the building industry, lived for much of his life on the island. He built the village hall in 1898 and his home 'Wylfa Manor' in 1896, on the site of the current power station. It is located under the current Wylfa car park.