In 1455, the land on which Craignethan was to be built transferred ownsership from the Black Douglases to the Hamilton family. In 1530, James Hamilton granted the land to his illegitimate son, who had earlier become an accomplished architect and military engineer. At Craignethan, he set out to display his talents in both domestic and military acrhitecture.
Despite his earlier favor with the Royal family, in 1540 this younger Hamilton was executed from treason and his properties were forefiet to the crown. The Hamlton family regained Craignethan Castle two years later, and the new owner, the second earl, added the large outer courtyard to the west of the castle.
By 1949, Craignethan Castle had passed in and out of the hands of the Hamiltons, as well as the Douglases, and later the Earls of Home. At this time, the property was given into state care and is now a Scheduled Ancient Monument managed by Historic Scotland.
Craignethan is built on an imposing site above a bend in the River Nethan. Steep slopes protect the castle on the south, north and east sides, but the castle is actually overlooked by higher ground to the west, making it far more vulnerable than it appears. Craignethan's defences are therefore concentrated towards the west. The castle comprises a low central keep, within a rectangular walled courtyard. To the west is a deep ditch and beyond, a larger outer courtyard.