Sedgefield is a market town and civil parish in County Durham, England. It had a population of 4,986 in the 2021 census. It has the only operating racecourse in County Durham.

The name Sedgefield is of Old English origin. It is derived from the given-name Cedd + feld (> "field").

In 2003, a Roman 'ladder settlement' was discovered in fields just to the west of Sedgefield, by Channel Four's Time Team programme. It consisted of rows of parallel crofts and workshops on either side of a north–south trackway, creating a ladder-like layout, which could be securely dated by the many finds of Roman coins.

During the 1800s, it was a hunting centre, dubbed 'the Melton of the North'. Hunter Ralph Lambton had his headquarters at Sedgefield: the humorous writer, Robert Smith Surtees, who lived at Hamsterley Hall, was a friend of his. On 23 February 1815, Lord Darlington wrote: 'Mr Ralph Lambton was out with some gentlemen from Sedgefield, and a most immense field.'

The town was known in the area because of Winterton Hospital. This was an isolation hospital and an asylum. The site was like a village itself with its own fire station, bank and cricket team. Today, little trace is left of the hospital, apart from the church, which is now surrounded by the Winterton housing estate and the NETPark Science park.

The population of the town at the time of the 1841 census was 1,345 inhabitants.

The 19th-century South African politician and industrialist Henry Barrington was born in Sedgefield, and actions by his offspring indirectly led to the South African town of Sedgefield, Western Cape, being named in honour of his birthplace.

Sedgefield constituency's Member of Parliament was Tony Blair; he was the area's MP from 1983 to 2007, Leader of the Labour Party from 1994 to 2007 and Prime Minister of the United Kingdom from 1997 to 2007.