The original house and estate were purchased by a wealthy merchant William Lemon (1696–1760) circa 1739. Lemon's town house in Truro had been designed by the architect Thomas Edwards, and it was again to Edwards that Lemon turned to substantially increase and modernise his new country house Carclew.
Work began in 1739, the enhancement to the mansion included flanking the main block with colonnades terminated by small pavilions in the fashionable Palladian manner, the design was similar in appearance to drawings of Palladio's planned Villa Ragona.
At the beginning of the 19th century William Lemon's grandson Sir William Lemon (1748–1824) had the house expanded further. He employed the architect William Wood (1746–1818) to create new wings in the place of the pavilions designed by Edwards. Work began in 1799 with the east wing being built in 1800 and the west wing in 1802. The wings were linked to the corps de logis by raised colonnaded connecting wings on the site of Edwards' original colonnades.
In 1934 Carclew was destroyed by fire and today just a few ruins are visible of what was once one of Cornwall's great houses. The terraced gardens complete with their water fountains and cascades remain and are open to the public.