A large Scots Baronial mansion of East Dunbartonshire, Lennox Castle overlooks Clachan of Campsie and the Campsie Fells, 1½ miles (2.5 km) west northwest of Lennoxtown. Built on a square plan, 1837-41, by David Hamilton (1768 - 1843) for John Lennox Kincaid, it comprises battlemented corner towers, with a larger tower in the centre of the west side and an entrance porch projecting from the north front. Kincaid's aunt, Margaret Lennox, had tried to prove her right to the Earldom of Lennox and, on her death in 1833, he inherited the estate, changed his name to Kincaid-Lennox and built the castle, next to the former Woodhead House, in an attempt to further his claim.
Glasgow Corporation bought the castle, along with 494 ha (1222 acres) of the estate, from the family for £25,000 in 1927 to serve as a hospital for the mentally-ill. New buildings were erected in the grounds to accommodate 600 males and 600 females in separate sections, each comprising a dining hall, kitchen, workshop and ten dormitory blocks. There was a central administration block, medical block, visitors' tea-room and an assembly hall, equipped with 'cinematographic sound apparatus', while the castle itself was used as a nurses home. Forty houses were built as staff married quarters.
The hospital formally opened on the 24th September 1936. In 1939, it was taken over as an Emergency War Hospital and the patients transferred to huts in the grounds. In 1941, a maternity unit was opened which sat uneasily with the main purpose of the hospital until the unit closed in 1964. The hospital reached its maximum of 1620 patients in the 1970s. The nurses' home closed in 1987 and the castle began to decline; internally it is in very poor condition. The hospital closed in phases from the 1990s until 2002, and all the buildings were then demolished, with the exception of the A-listed castle, to make was for housing. Celtic Football Club began building a training facility on part of the site in 2006.
The abandoned castle was badly damaged by fire in 2008.