Cadzow Castle, now in ruins, was constructed between 1500 and 1550 on the site of an earlier royal castle, one mile south-east of the centre of Hamilton, South Lanarkshire, Scotland. The town of Hamilton was formerly known as Cadzow or Cadyou (, the "" being the letter yogh), until renamed in 1455 in honour of James Hamilton, 1st Lord Hamilton. The castle sits above a gorge overlooking the Avon Water in what is now Chatelherault Country Park, but was previously the hunting and pleasure grounds of the Duke of Hamilton's estate of Hamilton Palace. The ruin is a category B listed building and a Scheduled Ancient Monument.