One of the best preserved and impressive castles in Ayrshire, Killochan Castle has a tall 16th century L-plan tower house which replaced an earlier castle on the site. The tower consists of a main block of five storeys and a higher wing. A square stair-tower stands in the re-entrant angle. A conical-roofed round tower at one corner has a corbelled-out parapet. Two bartizans crown the top of the tower. The entrance is defended by a machiolated projection at parapet level. The walls are pierced by shot-holes. The tower is dated 1586.
The entrance leads to a wide scale-and-plant stair, which climbs to the first floor, while the floors above were reached by a turnpike stair in the re-entrant angle. The basement is vaulted, and contained the original kitchen and two cellars. The hall is on the first floor and has an adjoining private chamber.
There is an 18th century wing of two storeys.
The property belonged to the Cathcarts from the 14th century. One of the family, Robert Cathcart of Killochan, was killed at the Battle of Flodden in 1513. In the feud between the Cassillis and Bargany Kennedys, the Cathcarts supported their neighbours of Bargany, and John Cathcart, builder of the castle, commanded the rear guard at a battle at Pennyglen, during which Bargany was mortally wounded. The Cathcarts occupied Killochan, although not continuously, until 1954.