William Herbert, 2nd Marquess of Powis DL (c. 1665 – 22 October 1745) was an English peer and Jacobite supporter.

After the Glorious Revolution, efforts on behalf of James II resulted in Montgomery's committal to the Tower of London on 6 May 1689 and he was not given bail until 7 November.

On 5 July 1690, and again on 23 March 1696 a proclamation, accompanied by a reward of £1,000, was issued for his apprehension; on the latter occasion, he was suspected of complicity in the Jacobite assassination plot.

Though he was reported to have given information concerning the plot, he remained there until 19 June 1697, when during an outbreak of gaol fever he was released on bail.

In January 1701 King William III allowed him to travel from Flanders in order to raise money on his estate and pay debts.

Financial difficulties led him to sell his house in Lincoln's Inn Fields to the Duke of Newcastle in May 1705.

Together, Mary and William had two sons and four daughters, including:[4] Lady Powis died on 8 January 1724 and was buried at Hendon, where the marquess had property.