Blessed William Lacy was an English Catholic martyr.

William was born at "Hanton", Yorkshire (probably Houghton or Tosside, West Riding); suffered at York, 22 August 1582. He married a widow, named Cresswell, whose sons, Arthur and Joseph, became Jesuits. Little is related of his family by his biographers. He had a brother Ralph of Preston in Amounderness, a sister Barbara, and nephews (apparently her sons) Robert and William (Cal. S. P., Dom. add. 1566-79, London, 1871, p. 562). He held a position of emolument under the Crown, possibly as coroner, till about 1565. One of this name, probably a relative, was a coroner for the West Riding in 1581-2 (Dasent, "Acts of the Privy Council", xiii, 358).

After fourteen years' persecution for his faith, which included imprisonment at Hull, and after the death of his wife, he went abroad and arrived at Reims, 22 June 1580. On 25 September following he went on to Pont-à-Mousson, and thence to Rome, where, after obtaining a dispensation, he became a priest. The dispensation was necessary before ordination, as Lacy had been married twice, once to a widow. On 10 May 1581, he was at Loreto on his way to England.