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 2 and a half miles south east of Aberaeron, Ceredigion, Wales. There is evidence that the house replaced an earlier mansion. A later owner, William Lewes was the husband of Colonel Lewis's inheriting daughter.
The estate is now in the care of the National Trust. The neighbouring parish church of St Non also redesigned by Nash has registers of baptisms and burials dating from 1730 and marriages from 1754.