It is unusual for a tower house of its age for its lack of defensive arrangements: it has no gun loops, its roof is without a parapet or corner turrets, and it lies in open ground without natural defences.

Earlstoun Castle lies on the edge of a shallow bank in open countryside about 3 kilometres (2 mi) north of St John's Town of Dalry.

[4] It lacks many of the defensive features that might normally be expected on a building of its age and type, such as gun loops, a parapet and corner turrets, and its situation in open ground offers no natural protection.

[3][2] The hall, which runs the full length of the main wing on the first floor, has large windows, and retains some of its ornate Renaissance panelling and cornicing, and a fireplace with Ionic pilasters in the north east gable wall, but these are all now in a state of considerable disrepair.

A two-storey extension was built onto the north-east wall, in which was set a stone dated 1655 with the initials WG/MH, for William Gordon of Earlston and his wife, Mary Hope.

[1] Around this time, the windows of the first floor were enlarged, the elaborate Renaissance panelling was installed in the great hall, and the arrangement of fireplaces and the orientation of some of the rooms was altered.