After Elizabeth de Clare's death, Clare Castle passed by marriage to the son of Edward III, Lionel of Antwerp, and again by marriage to the Mortimers of Wigmore.
When Sir Edmund Mortimer acquired the castle in 1405, contemporaries reported it "in good repair and stocked".
The subsequent years saw the Mortimers heavily involved in the Wars of the Roses; after Edmund's death in 1425, the castle passed to Richard of York and in turn, via his son Edward IV, to the Crown.
Early in the reign of Edward IV, on 1 June 1461, the castle was part of a large estate gifted by the king to his mother, Cecily Neville, dowager Duchess of York, who did use the castle, but not as a main residence.
Her half sister, Margaret Neville Scrope, resided in the castle until her death in 1463, and was buried at Clare Priory.

The castle deteriorated during this period.
The masonry of the castle had probably been stripped for use as local building materials, as this part of England was traditionally very short of suitable stone.
Edward VI gave the castle to Sir John Checke, until it reverted to Mary I. After Mary, the castle was acquired by Sir Gervase Elwes, whose family retained it until the 19th century.
At some point after 1720, the surviving east and south sides of the inner bailey walls were destroyed.

In 1867 the Cambridge and Colchester branch line of the Great Eastern Railway was built through the castle, cutting across and largely destroying the inner bailey in order to make room for a new station.
The railway line was later closed in 1967 as part of the Beeching Axe.

The castle now consists of a motte, on which a part of the keep still stands and the outer bailey earthworks; fragments of the inner bailey stone wall can also still be seen.
The disused station, goods yard and the castle grounds have been developed into a landscaped country park, interlaced with water in the old moats, called Clare Castle Country Park, which is crossed by the Stour Valley Path.
The park was opened in June 1972, after 15 acres (6.1 ha) were donated by Anthony de Fontblanque and 4.5 acres (1.8 ha) of railway land bought for £10,000.
 In 2014, the keep and curtain wall were extensively consolidated with the assistance of English Heritage.
In March 2015, the stewardship of the park transferred from Suffolk County Council to the Clare Town Council; a trust manages the park with the support of local volunteers.
The castle is protected under UK law as a scheduled monument and a grade 2* listed building.
After Elizabeth de Clare's death, Clare Castle passed by marriage to the son of Edward III, Lionel of Antwerp, and again by marriage to the Mortimers of Wigmore. When Sir Edmund Mortimer acquired the castle in 1405, contemporaries reported it "in good repair and stocked". The subsequent years saw the Mortimers heavily involved in the Wars of the Roses; after Edmund's death in 1425, the castle passed to Richard of York and in turn, via his son Edward IV, to the Crown. Early in the reign of Edward IV, on 1 June 1461, the castle was part of a large estate gifted by the king to his mother, Cecily Neville, dowager Duchess of York, who did use the castle, but not as a main residence. Her half sister, Margaret Neville Scrope, resided in the castle until her death in 1463, and was buried at Clare Priory.
The castle deteriorated during this period. The masonry of the castle had probably been stripped for use as local building materials, as this part of England was traditionally very short of suitable stone. Edward VI gave the castle to Sir John Checke, until it reverted to Mary I. After Mary, the castle was acquired by Sir Gervase Elwes, whose family retained it until the 19th century. At some point after 1720, the surviving east and south sides of the inner bailey walls were destroyed.
In 1867 the Cambridge and Colchester branch line of the Great Eastern Railway was built through the castle, cutting across and largely destroying the inner bailey in order to make room for a new station. The railway line was later closed in 1967 as part of the Beeching Axe.
The castle now consists of a motte, on which a part of the keep still stands and the outer bailey earthworks; fragments of the inner bailey stone wall can also still be seen. The disused station, goods yard and the castle grounds have been developed into a landscaped country park, interlaced with water in the old moats, called Clare Castle Country Park, which is crossed by the Stour Valley Path. The park was opened in June 1972, after 15 acres (6.1 ha) were donated by Anthony de Fontblanque and 4.5 acres (1.8 ha) of railway land bought for £10,000.  In 2014, the keep and curtain wall were extensively consolidated with the assistance of English Heritage. In March 2015, the stewardship of the park transferred from Suffolk County Council to the Clare Town Council; a trust manages the park with the support of local volunteers. The castle is protected under UK law as a scheduled monument and a grade 2* listed building.
Clare Castle