Trewithen is one of the largest privately owned estates in Cornwall. About one third of the estate surrounds the house, the parklands and gardens between Grampound, Grampound Road, Probus and Tregony and includes the romantic and very historic Golden Valley through which the Fal River runs.
The rest of the estate is centred around the villages of St Newlyn East, Mitchell and Zelah and from there over to the Gannel River near Newquay. There are further areas near St Austell and St Just in Roseland on the Roseland Peninsula.
Largely agricultural, much of the estate is let to farmers through Farm Business Tenancies and traditional Agricultural Holdings Act agreements. The mixed farming carried out includes dairy, stock and arable, and crops such as potatoes, brassicas and maize are grown. There is also a wind farm, a solar farm, a rifle range, a nine hole golf course, an explosives store and a boatyard among the other diversified businesses on the estate.