St Allen parish was in the Western division of the Hundred of Powder, in the Deanery of Powder and is surrounded by St Erme, St Clements, Kenwyn, Perranzabuloe and Newlyn East; it is now in the Carrick district and is situated to the North of Truro. There are a number of small hamlets and farmsteads dotted around the parish. The principal settlement in the parish is Zelah.