William Sarsfield

Sir William Sarsfield was an Irish landowner, public official and soldier of the sixteenth century.

Sarsfield was from a wealthy merchant family, part of the Old English inhabitants of The Pale who remained Roman Catholic following the Reformation. Sarsfield served as Mayor of Dublin. He was knighted in 1566 for his service against Shane O'Neill, the rebellious Gaelic lord of Tyrone.

He purchased estates at Tully Castle in County Kildare and Lucan Manor in County Dublin. He was the grandfather of Peter Sarsfield of Tully. Among his many other descendants was his great-great-grandson Patrick Sarsfield, who famously fought on the Jacobite side during the Williamite War in Ireland (1689–91).