Johnstone Castle belonged to the Houstouns of Milliken, who acquired the estate of Easter Cochrane in 1773. The original structure was substantially enlarged in 1771 and 1812 by George Houstoun.
Johnstone Castle's principal claim to fame is a visit by the Polish composer Chopin in 1848. He had been invited by Anne Houstoun, wife of the then-laird Ludovic, as part of his Scottish tour.