Derbyshire (/ˈdɑːrbiʃɪər, -ʃər/ DAR-bee-sheer, -⁠shər) is a ceremonial county in the East Midlands of England. It borders Greater Manchester, West Yorkshire, and South Yorkshire to the north, Nottinghamshire to the east, Leicestershire to the south-east, Staffordshire to the south and west, and Cheshire to the west. Derby is the largest settlement, and Matlock is the county town.

The county has an area of 2,625 km² (1,014 sq mi) and a population of 1,066,954 in 2022. The eastern half of the county is more densely populated than the west contains its largest settlements: Derby in the south-east, Chesterfield in the north-east, and Swadlincote in the south. For local government purposes Derbyshire comprises a non-metropolitan county, with eight districts, and the Derby unitary authority area. The East Midlands Combined County Authority includes Derbyshire County Council and Derby City Council.

The north and centre of Derbyshire are hilly and contain the southern end of the Pennines, most of which are part of the Peak District National Park. They include Kinder Scout, at 636 m (2,087 ft) the highest point in the county. The River Derwent is the longest in the county, at 66 miles (106 km), and flows south until it meets the River Trent just south of Derby. Church Flatts Farm at Coton in the Elms, near Swadlincote, is the furthest point from the sea in the UK.

The area that is now Derbyshire was first visited, probably briefly, by humans 200,000 years ago during the Aveley interglacial, as shown by a Middle Paleolithic Acheulean hand axe found near Hopton. Further occupation came with the Upper Paleolithic and Neolithic periods of the Stone Age when Mesolithic hunter-gatherers roamed the hilly tundra. Evidence of these nomadic tribes has been found in limestone caves located on the Nottinghamshire border. Deposits left in the caves date the occupancy at around 12,000 to 7,000 BCE.

Burial mounds of Neolithic settlers are also situated throughout the county. These chambered tombs were designed for collective burial and are mostly located in the central Derbyshire region. There are tombs at Minninglow and Five Wells that date back to between 2000 and 2500 BCE. 5 kilometres west of Youlgreave lies the Neolithic henge monument of Arbor Low, which has been dated to 2500 BCE. It is not until the Bronze Age that real signs of agriculture and settlement are found in the county. In the moors of the Peak District signs of clearance, arable fields and hut circles were found after archaeological investigation. However this area and another settlement at Swarkestone are all that have been found.

During the Roman conquest of Britain, the invaders were attracted to Derbyshire for its lead ore in the limestone hills of the area. They settled throughout the county, with forts built near Brough in the Hope Valley and near Glossop. Later they settled round Buxton, famed for its warm springs, and set up a fort near modern-day Derby in an area now known as Little Chester.

Several kings of Mercia are buried in the Repton area.

Following the Norman Conquest, much of the county was subject to the forest laws. To the northwest was the Forest of High Peak under the custodianship of William Peverel and his descendants. The rest of the county was bestowed upon Henry de Ferrers, a part of it becoming Duffield Frith. In time the whole area was given to the Duchy of Lancaster. Meanwhile, the Forest of East Derbyshire covered the whole county to the east of the River Derwent from the reign of Henry II to that of Edward I.