Dartford is the principal town in the Borough of Dartford, Kent, England. It is located 18 mi (29 km) south-east of Central London and is situated adjacent to the London Borough of Bexley to its west. To its north, across the Thames Estuary, is Thurrock in Essex, which can be reached via the Dartford Crossing. To its east lies the Borough of Gravesham and to the south the district of Sevenoaks. It had a population of 51,240.

The town centre lies in a valley through which the River Darent flows and where the old road from London to Dover crossed: hence the name, which derives from Darent + ford. Dartford became a market town in medieval times and, although today it is principally a commuter town for Greater London, it has a long history of religious, industrial and cultural importance. It is an important rail hub; the main through-road now by-passes the town itself.

Dartford lies within the area known as the London Basin. The low-lying marsh to the north of the town consists of London Clay and the alluvium brought down by the two rivers—the Darent and the Cray—whose confluence is in this area. The higher land on which the town stands and through which the narrow Darent valley runs, consists of chalk surmounted by the Blackheath Beds of sand and gravel.

As a human settlement, Dartford became established as a river crossing-point with the coming of the Romans; and as a focal point between two routes: that from west to east being part of the main route connecting London with the Continent; and the southerly route following the Darent valley. As a result, the town's main road pattern makes the shape of letter 'T'. The Dartford Marshes to the north and the proximity of Crayford in the London Borough of Bexley to the west, mean that the town's growth is to the south and east. Wilmington is contiguous with the town to the south; whilst the almost continuous Thames Gateway development means that there is little to show the town boundary in an easterly direction.

Within the town boundaries there are several distinct areas: the town centre around the parish church and along the High Street; the Joyce Green area; Temple Hill estate constructed in 1947; the Brent; Fleet Downs; as well as two important areas of open space and several industrial estates. The open spaces are Central Park, alongside the river; and Dartford Heath.

Like most of the United Kingdom, Dartford has an oceanic climate.

In prehistoric times, the first people appeared in the Dartford area around 250,000 years ago: a tribe of prehistoric hunter-gatherers whose exemplar is called Swanscombe Man. Many other archaeological investigations have revealed a good picture of occupation of the district with important finds from the Stone Age, the Bronze Age and the Iron Age.

When the Romans engineered the Dover to London road (afterwards named Watling Street), it was necessary to cross the River Darent by ford, giving the settlement its name. Roman villas were built along the Darent Valley, and at Noviomagus (Crayford), close by. The Saxons may have established the first settlement where Dartford now stands. Dartford manor is mentioned in the Domesday Book, compiled in 1086, after the Norman conquest. It was then owned by the king.