Penkill Castle stands about three miles east of Girvan. The oldest part was constructed about 1490, with the original doorway about 15 feet above the ground.

The tower was built by Adam Boyd, grandson of Robert, Lord Kilmarnock. The first addition was built by Thomas Boyd, Adam's great-great-grandson.

In 1857, Penkill was in poor condition. It was extensively rebuilt by Spencer Boyd. The castle passed out of the Boyd family in the 1960s with furnishings intact. But these were unfortunately dispersed by the 1980s.