County Durham is a county in the north east of England. It's county town (capital) is Durham. It is a county of contrasts: the remote and sparsely populated dales and moors of the Pennines characterise the interior, while nearer the coast the county is highly urbanised, and was once dominated by the coal mining industry.

County Durham's historic boundaries are the watershed of the Pennines in the west, the River Tees in the south, the North Sea in the east and the Rivers Tyne and Derwent in the north.

In the north, the boroughs of Gateshead, Sunderland and South Tyneside, now form part of the metropolitan county of Tyne and Wear, whilst in the south, Hartlepool, Darlington, and Stockton-on-Tees form separate unitary authories within the ceremonial county of Durham (Stockton is also partly in the ceremonial county of North Yorkshire). A part of the historic North Riding of Yorkshire, south of the River Tees, the former area of Startforth Rural District, is included in the Durham district of Teesdale.

Durham County Council promotes the county for tourism purposes as "The Land of the Prince Bishops" in reference to the former palatine jurisdiction of the bishops.

The form of the county name is unique in England. Many counties are named after their principal town, and the expected form here would be Durhamshire. The reason it is called County Durham instead is that the Bishops of Durham historically exercised power in regions outside the county as well, so the inner part was named County Durham as opposed to the rest of the estate of Durham. The form County X is standard for Irish counties, with no such significance or relationship.

According to a marketing campaign by the charity Plantlife, County Durham's county flower is the Spring Gentian.