Eynsford Castle originally comprised an inner and an outer bailey, overlooking the River Darent.
The outer bailey lay to the south-east of the surviving remains of the castle, but little is known about its shape or the buildings within it.
The inner bailey survives as a low earth terrace, or mound, forming an irregular polygon up to 61 metres (200 ft) across, protected by a curtain wall and a moat.
Its curtain wall is 9 metres (30 ft) high and almost 2 metres (6 ft 7 in) wide, made of coursed flint rubble reinforced with mural timbers, with ironstone slabs in the putlog and drawbar holes used in its construction.
It was built in two phases, the first two thirds in the 11th century, and the upper 3.7 metres (12 ft) in  1130, in part reusing Roman tiles, and it was equipped with three sets of garderobes.
The north side of the wall collapsed in the 19th century, and the terrace edge is stabilised by a modern concrete wall.

The inner bailey is reached using a bridge over the moat.
The original castle bridge was constructed from wood but this was rebuilt with stone facades and piers in the late medieval period, and then subsequently replaced with an earth bank, further improved in the early 19th century; the current timber bridge dates from the 1960s.
A gate house originally protected the entrance, with an arched passageway made from Roman brick, flanked by guardrooms; only the foundations now survive.

In the north-west corner of the bailey are the foundations of the great kitchen.
The north-east corner is occupied by the remains of the 12th-century hall complex, built from flint stone, with green sandstone dressings and Roman tiles, and comprising a solar, a hall and forebuildings, of which only the foundations now survive.
The solar itself was located on the first floor of the building, with its undercroft forming a separate apartment, probably for the use of the castle bailiff.
The first floor of the hall would have been used for public business and living space, and the undercroft used for storage or living space.
The forebuilding was 8.5 by 18.3 metres (28 by 60 ft) internally, linked to the hall by a passageway, and provided additional space, and a kitchen was located at the rear of the hall.
Eynsford Castle originally comprised an inner and an outer bailey, overlooking the River Darent. The outer bailey lay to the south-east of the surviving remains of the castle, but little is known about its shape or the buildings within it. The inner bailey survives as a low earth terrace, or mound, forming an irregular polygon up to 61 metres (200 ft) across, protected by a curtain wall and a moat. Its curtain wall is 9 metres (30 ft) high and almost 2 metres (6 ft 7 in) wide, made of coursed flint rubble reinforced with mural timbers, with ironstone slabs in the putlog and drawbar holes used in its construction. It was built in two phases, the first two thirds in the 11th century, and the upper 3.7 metres (12 ft) in  1130, in part reusing Roman tiles, and it was equipped with three sets of garderobes. The north side of the wall collapsed in the 19th century, and the terrace edge is stabilised by a modern concrete wall.
The inner bailey is reached using a bridge over the moat. The original castle bridge was constructed from wood but this was rebuilt with stone facades and piers in the late medieval period, and then subsequently replaced with an earth bank, further improved in the early 19th century; the current timber bridge dates from the 1960s. A gate house originally protected the entrance, with an arched passageway made from Roman brick, flanked by guardrooms; only the foundations now survive.
In the north-west corner of the bailey are the foundations of the great kitchen. The north-east corner is occupied by the remains of the 12th-century hall complex, built from flint stone, with green sandstone dressings and Roman tiles, and comprising a solar, a hall and forebuildings, of which only the foundations now survive. The solar itself was located on the first floor of the building, with its undercroft forming a separate apartment, probably for the use of the castle bailiff. The first floor of the hall would have been used for public business and living space, and the undercroft used for storage or living space. The forebuilding was 8.5 by 18.3 metres (28 by 60 ft) internally, linked to the hall by a passageway, and provided additional space, and a kitchen was located at the rear of the hall.
Eynsford Castle