St Mellion is also the location of Pentillie, a 17th-century castle and estate which has been the seat of the Coryton family since 1698. They had previously had an estate at West Newton Ferrers, also in St Mellion. The manor of Newton Ferrers (Niuuetona, Niweton, Niwetone) is recorded in the Domesday Book of 1086.[4] Part of the manor was held by Reginald from Robert, Count of Mortain. There was half a hide of land and land for six ploughs. There were two ploughs, three serfs, three villeins, 12 smallholders, 12 acres of pasture, five cattle, 40 sheep and 10 goats. The value of this part was £1 though it had formerly been worth £1 10s.
The other part of the manor was also held by Reginald from Robert, Count of Mortain. There was one hide of land and land for eight ploughs. There were 10 villeins and 20 smallholders with one plough, three serfs, half a league of pasture, woodland two leagues long and one furlong wide. The value of this part was £1 10s. though it had formerly been worth £2.
The present house was built about 1686–95 (these dates being on the gatepiers) for Sir William Coryton. It is a plain granite mansion of two storeys: the centre is of seven bays and there are two projecting wings of two bays each. It is the earliest Cornish mansion in the classical style (i.e. with no Tudor survivals). Two thirds of the house were gutted by fire in 1940; of this some has been rebuilt while the rest remains as a ruin. The St Mellion golf course is also in the parish.
Crocadon Quarry, 200 metres east of St Mellion village, is a Site of Special Scientific Interest for its geology.[8]