It is well-preserved and occupied.
From the 14th century the Cathcart family owned the property. Robert Cathcart of Killochan died at the battle of Flodden in 1513. When the Kennedys of Cassillis and Bargany feuded the Cathcarts supported their Bargany neighbours, with John Cathcart, who built the castle, commanding the rearguard at the battle of Pennyglen.
The present castle, dating from 1581, probably replaces an earlier one on the same, or a nearby, site. A wing was added in the 18th century. The castle was occupied by the Cathcart family, intermittently, until 1954.
Killochan castle has been described as one of the finest fortified houses in south Scotland. The castle has a five-storey main block, lying east to west, with a higher wing extending northward at the east end. In the re-entrant angle there is a square stair tower, while there is a round tower, with a corbelled-out parapet at one corner. The top of the tower is crowned by two bartizans.
A wide scale-and-platt stair leads from the entrance to the first floor; whence other floors may be reached by way of a turnpike stair in the re-entrant angle. The hall, and an adjoining chamber, are on the first floor.
The 18th-century wing has two storeys.
It is a Category A Listed Building.