William Tirry (1609 – 12 May 1654) was a martyred Irish Roman Catholic priest who was beatified by Pope John Paul II for his loyalty to the church.
Tirry was born in County Cork, Ireland in 1608, the nephew of the elder William Tirry, Bishop of Cork and Cloyne, and grandson of Edmond Terry, or Tirry, Lord Mayor of Cork, and his wife Catherine Galway. His aunt Joan married Dominick Sarsfield, 1st Viscount Sarsfield, the Chief Justice of the Irish Common Pleas: their son William, the 2nd Viscount, played an important role in Tirry's life as his patron and protector.
He joined the Augustinian Order in Cork and studied in Valladolid, Spain and Paris, France. Upon completion of his education in Paris, he spent five years (1636–1641) in Brussels, Belgium.
He returned to Ireland in 1641. For several years he found a safe refuge with his cousin William Sarsfield, 2nd Viscount Sarsfield, who was a Roman Catholic, and acted as tutor to his sons. Lord Sarsfield's death in 1648 deprived Tirry of his chief protector. In 1649 he was chosen as Prior (local superior) of the Augustinian house in Skreen. This was the same year that marked the beginning of the Cromwellian conquest of Ireland. A law was enacted on 6 January 1653 declaring that any Roman Catholic priest in Ireland was guilty of treason. Tirry was forced into hiding alongside other priests, but was captured when three men reported his whereabouts for money.