The castle sits north of Baconsthorpe village in a valley formed by the River Glaven, approached by the remains of a raised causeway from the south. The Heydons built the inner court on a square earth platform 65 metres across, surrounded by a water-filled moat up to 15 metres wide and an external curtain wall up to 5 metres high, protected by seven square and circular mural towers. The main entrance passed through an inner gatehouse three storeys high, built from knapped flint and brick — an expensive material choice that underscored the family's aspirations.

The militarily inspired design drew deliberately on earlier medieval architectural traditions. Gun loops covered the entrance from the cellar beneath the hall. A postern gate in the north tower led to a bridge over the moat. The whole composition was theatre as much as defence. The eastern side of the inner court was adapted for the wool industry in the 16th century, with a long two-storey building constructed along the curtain wall for processing and fulling cloth — a reminder that the fortune funding this grandeur came from trade.

The Heydon family's finances declined over generations. When civil war broke out in 1642, one John Heydon fought for King Charles I. Parliament responded by seizing his lands and declaring him delinquent in 1646. He died in debt in 1653, leaving the castle to his son Charles Heydon. The stripping of the castle began almost immediately: 29 cartloads of stone were sold the following year for £30, destined for reuse at nearby Felbrigg Hall.

The outer gatehouse — a Perpendicular Gothic structure with octagonal turrets and a large first-floor chamber — was converted to residential use in the 17th century. Wings were added, a three-storey porch built onto the front, and the building took on a new life as a domestic residence. A doctor named Zurishaddai Lang lived in it. The Norfolk landowner John Thruston Mott bought the estate in 1801, and the gatehouse remained occupied until 1920, when one of the turrets collapsed. By then the moat had been drained and the castle's working life was over.

In 1940, the owner Sir Charles Mott-Radclyffe placed the site under the care of what was then the Ministry of Public Works. The mere was dredged and refilled in 1972. Archaeological excavations have since revealed more of the castle's layout, including the remains of a formal garden to the south-east of the inner court — a raised platform 80 metres across, with a raised walkway around a square pond 35 metres wide.

Today Baconsthorpe Castle is managed by English Heritage and carries Grade I and Grade II listed building status, as well as scheduled monument protection. The ruins rise from fields that were once sheep pasture in the 16th century and are now used mainly for arable farming. The flint and brick towers stand in the Norfolk silence, reflecting in the refilled moat, the whole ensemble a study in how quickly a family's assertion of permanence can dissolve into landscape.