Sir William Penn (1621–1670) was an English admiral, and the father of William Penn, founder of the colony of Pennsylvania.

In the First Anglo-Dutch War, he served in the navy of the Commonwealth of England, commanding squadrons at the battles of the Kentish Knock (1652), Portland, the Gabbard and Scheveningen (1653).

At the Restoration he was sent in the Naseby (later the Royal Charles) to fetch king Charles II over to England.

In the Second Anglo-Dutch War he was captain of the fleet at the Battle of Lowestoft in 1665 under James Stuart, Duke of York.

He is mentioned numerous times in the diary of Samuel Pepys.