Llanerchaeron, known as "Llanayron House" to its nineteenth-century occupants, is a grade I listed mansion on the River Aeron, designed and built in 1795 by John Nash for Major (later Colonel) William Lewis as a model, self-sufficient farm complex located near Ciliau Aeron, some 2½ miles south-east of Aberaeron, Ceredigion, Wales. There is evidence that the house replaced an earlier mansion.