Llanveyr 1254, Lanveyr c.1291, 1293, - in Kereynon 1281-2, Lanvar 1338, Llanvaire 1535, ll.fair c.1566, Llanvair 1577, - in Krynion 1579, Llanfair in Karinion 1585-6, Llanvyer in Kaereinion 1593-4, Llanfair, or Llan Fair yn Nghaer Einion 1813.

Church of (St). Mary in Caereinion' with llan 'church', Mair and the name of its cant ref or hundred Caereinion. Many spellings with 'in' may stand for the Welsh preposition yn(g), 'in' suggesting that its full name was Llanfair yng Nghaereinion to Welsh-speakers. Caereinion is usually explained in English as 'Einion's fort' with Welsh caer 'fort, fortress' but it may actually contain a personal name *Ceraint or Cerain and a suffix - ion found in territorial names such as Ceredigion and Mebwynion.