William Jephson (1609 – 11 December 1658) was an English politician who sat in the House of Commons from 1640 to 1648. He was served in the Parliamentary army and was Cromwell's envoy to Sweden.
Jephson was the son of Sir John Jephson and his wife Elizabeth Norreys, daughter of Sir Thomas Norreys, Lord President of Munster. She brought the Irish estates at Mallow and elsewhere to the Jephson family.
In April 1640, Jephson was elected Member of Parliament for in the Short Parliament. He was re-elected in November 1640 for the Long Parliament. Jephson was a member of Hampshire Committee in 1644 and also Lieutenant Governor of Portsmouth in 1644 Jephson was not recorded as sitting in parliament after Pride's Purge in 1648. He sold the Froyle estate in 1653. Jephson became a major general and was the representative in parliament for Cork in the First Protectorate Parliament in 1654 and in the Second Protectorate Parliament in 1656. In 1657 Oliver Cromwell sent him as envoy to Sweden while Sweden was at war with Denmark.
Jephson married Alicia Denham, daughter of Sir John Denham. His son William was later MP for East Grinstead and Wycombe.