William Jessop (23 January 1745 - 18 November 1814) was a noted English civil engineer, particularly famed for his work on canals, harbours and early railways in the late 18th and early 19th centuries.

Jessop was born in Devonport, Devon in 1745, the son of a shipwright known to leading civil engineer John Smeaton through his work on the Eddystone Lighthouse. When Jessop's father died, William Jessop was taken on as a pupil by Smeaton (who also acted as Jessop’s guardian), working on various canal schemes in Yorkshire. After working for some years as Smeaton's assistant, Jessop increasingly began to work as an engineer in his own right.

In 1790, he founded (with fellow engineer Benjamin Outram) an iron-works in Derbyshire, the Butterley Iron Works, to manufacture cast-iron edge rails – a design Jessop had used successfully with flanged wheels on a horse-drawn railway scheme for coal wagons in Loughborough, Leicestershire (1789).

His projects included:

• the Calder and Hebble Navigation (1758-70)
• the Aire and Calder Navigation
• the Ure and Ripon Canal (1767)
• the Barnsley Canal (1792-1802)
• Grand Canal of Ireland between the River Shannon and Dublin (1773-1805)
• the Grand Junction Canal (1793-1805 - later known as the Grand Union Canal)
• the Cromford Canal, Derbyshire/Nottinghamshire
• the Nottingham Canal (1792-1796)
• River Trent Navigation
• the Grantham Canal (1793-1797 - the first English canal entirely dependent on reservoirs for its water supply)
• oversight of the Ellesmere Canal – (1793-1805 - detailed design undertaken by Thomas Telford)
• Rochdale Canal (1794-1798)
• West India Docks and Isle of Dogs canal, London (1800-1802)
• the Surrey Iron Railway, linking Wandsworth and Croydon (1801-1802 – arguably Britain's first public railway – albeit horse-drawn)
• the 'Floating Harbour' in Bristol (1804-1809)
• harbours at Shoreham-by-Sea and Littlehampton, West Sussex

Jessop lived for some years (1784-1805) in Newark in Nottinghamshire, where he also twice served as town mayor.