The great house stands in extensive grounds (360 hectares or 890 acres) above the River Fowey and it has been owned and managed by the National Trust since 1953. Much of the present house dates back to Victorian times but some sections date from the 1620s. It is a Grade I listed building and is set in gardens with formal areas. The hill behind the house is planted with a fine selection of shrubs and trees.
The parish church is dedicated to St Hydroc and stands in the grounds of Lanhydrock House. Parts date back to the late 15th century and the church has a chancel, nave, north and south aisles and three-stage battlemented tower with nine bells. Eight bells date from the late 19th century and are regularly rung. The ninth bell dates from circa 1599 and is only rung infrequently for tolling.
Lanhydrock estate belonged to the Augustinian priory of St Petroc at Bodmin but the Dissolution of the Monasteries during the 1530s saw it pass into private hands. In 1620 wealthy merchant Sir Richard Robartes, of Truro, acquired the estate and began building Lanhydrock House, designed to a four-sided layout around a central courtyard and constructed of grey granite. Robartes died in 1624 but work on the building was continued by his son John Robartes, 1st Earl of Radnor, a notable public figure who served as Lord Privy Seal and Lord President of the Council. The embattled walls were built of rude (rough), massive granite blocks with years 1636 and 1642 on the walls, indicating when they were built. A barbican gate was added and the house was garrisoned by Parliamentary forces in August 1644 when Sir Richard Grenville took possession.
Most of the current building dates from late Victorian times, when the estate came under the ownership of the Agar-Robartes family.
Through a lack of children, by the late 18th century the estate had passed to Anna Maria Hunt (1771–1861) of Mayfair, London, the great-niece of Henry Robartes, 3rd Earl of Radnor and 4th Baron Robartes. In 1804 she married Charles Bagenal Agar, the youngest son of Irish peer James Agar, 1st Viscount Clifden. The couple had three children, but by 1818 not only had her husband died, but also her eldest and youngest sons. Resultantly, over the next 50 years of widowhood, although mainly a remote landlord – she preferred the social life of London – she was known to be a conscientious, benevolent and charitable landlord and employer, who greatly improved the estate. On the death of his mother in 1822, her surviving middle son Thomas Agar moved his home to the estate, and adopted the Robartes name by warrant. Agar-Robartes was returned to Parliament for Cornwall East in 1847, a seat he held until 1868. In 1869 the barony of Robartes held by his mother’s ancestors was revived when he was raised to the peerage as Baron Robartes of Lanhydrock, and of Truro in the County of Cornwall. By 1872 Baron Robartes of Lanhydrock, was listed in the top ten land holdings in Cornwall with an estate of 22,234 acres (89.98 km2) or 2.93% of Cornwall.
Agar-Robartes had had the east wing of the house demolished, leaving the U-shaped plan seen today. In 1880 he commissioned the architect George Gilbert Scott to renovate Lanhydrock House. On 4 April 1881 a major fire destroyed the south wing and caused extensive damage to the central section. The fire started in the kitchen and the near gale-force wind fanned the flames along the south wing and the ″communicating block″. Of the main house only the north wing, with its 116 feet (35 m) Long Gallery, and the front porch building survived intact, along with the original gatehouse which also dates back to the mid-17th century. The gallery was decorated with old plaster work which was considered to be the finest of its type in the west of England with figures representing the creation in ″bas-relief″. The property was insured for £10,000 in the Royal Standard Office and for £10,000 in the County Fire Office and the damage is estimated to cost £8,000 to £10,000 It was reported in August 1881 that the rebuilding of the house would cost £50,000 and was to be undertaken by Messers Lang and Son of Liskeard. New sections were built behind the south wing, including a kitchen block, in the style of the original building – which was unusual at the time. Agar-Robartes wife died five days after the fire of smoke inhalation, and he died of a broken heart 12 months later.
Their only son Thomas Charles Agar-Robartes, 6th Viscount Clifden inherited the estate. He appointed local architectRichard Coad – who had worked as an assistant to George Gilbert Scott – to design and supervise the construction of a high-Victorian home from the previous adaptions of a Jacobean house his father had planned. After renovations on the home were completed, Agar-Robartes moved his family there from 1885. Having been called to the Bar in 1870, in 1880 Agar-Robartes was returned to Parliament as one of two representatives for Cornwall East. He entered the House of Lords on the death of his father in 1882, and on 10 September 1899 succeeded his kinsman as sixth Viscount Clifden. In 1891, as chairman of the Agar-Robartes Bank he took over the ownership of Wimpole Hall, the largest house in Cambridgeshire. Moving his family home there, he later served as Lord-Lieutenant of Cambridgeshire from 1906 to 1915.
The Robartes family declined significantly during the First World War, including the heir Thomas Agar-Robartes MP, who was killed during the Battle of Loos in France, while trying to rescue a colleague from no-man’s land. Only one descendant survives, living in a cottage on the estate.