In 1608 Sir Aulay MacAulay represented the County of Dumbarton in the Scots Parliament. He was one of two Commissioners appointed to regulate the price of boots and shoes, and his coat-of-arms indicates this. The fortunes of the MacAulays slowly declined and the land and Castle passed to the Duke of Argyll and through him to Lord John Campbell, and then to Sir James Colquhoun.

In the 1740s, Archibald MacAulay, Laird of Ardencaple, had to sell off a portion of his estate, though by the early 1750s the roof had fallen in and the overall condition of the castle had deteriorated to such an extent that the next Laird was forced to abandon his residence there and live in nearby Laggarie. In about 1767, the 12th chief, Aulay MacAulay of Ardencaple, died at High Laggarie (now within the present village of Rhu).