William Herbert, 1st Marquess of Powis, PC (1626 – 2 June 1696) was an English nobleman, best remembered for his suffering during the Popish Plot. He succeeded his father as 3rd Baron Powis in 1667 and was created Earl of Powis in 1674 by King Charles II and Viscount Montgomery, of the Town of Montgomery, and Marquess of Powis in 1687 by King James II, having been appointed to the Privy Council in 1686.