William Boyd, 4th Earl of Kilmarnock (12 May 1705 – 18 August 1746), was a Scottish peer who joined the 1745 Jacobite Rising, was captured at Culloden and subsequently executed for treason on Tower Hill.

"[1] His title was declared forfeit and his heavily mortgaged estates confiscated; they were later returned to his eldest son James, later Earl of Erroll, who fought at Culloden on the government side.

Educated at the University of Glasgow, Kilmarnock reportedly had "an Aversion to rigorous Study of Letters" and was devoted to "Riding, Fencing, Dancing and Musick...esteemed by Men of Taste, a Polite gentleman.

[5] The Earl and the Countess lived at Dean Castle in Kilmarnock (Ayrshire), but when it was destroyed by fire in 1735 they could not afford the repairs and moved to Anne's home, Callendar House (in Falkirk), which remained in the family until 1783.

The decision to join the Jacobite army surprised many; it has been suggested one reason for doing so was pressure from his wife's family but he later told Argyll; "...I was starving, and...if Mahommed had set up his standard...I had been a good Mussulman for bread, for I must eat.

One of the few Lowland peers to join the Rising, he quickly gained a prominent position with Charles, largely because he was unconnected to the group of long-term Jacobite Scots centred around Lord George Murray.

The claim he was captured after mistaking government dragoons for his own troops is not supported by his own account; another anecdote recounts he lost his hat and wig and James gave him his own.

[18] Cromartie's father-in-law had been Private Secretary to the Prince of Wales and the writer Horace Walpole (1717-1792) later observed "Hamilton's intercession for Lord Kilmarnock hurried him to the block.

However, Balmerino ensured Kilmarnock confirmed before witnesses that if such an order did exist, the blame lay with Lord George Murray, not the Prince, a version later published in the official trial records.