Repairs were made to the castle between 1610 and 1611 by the captain, Sir George Bampfield, at a cost of £211.
A survey in 1623 carried out by Sir Richard Morryson showed the castle to be equipped with ten iron guns – one culverin, five demi-culverins, two sakers, a minion and a falcon – and garrisoned by its captain, five gunners and three soldiers.
It was in a poor condition, and one corner of the gun platform had been undermined by the sea; Morryson's team estimated the likely costs of repairs to amount to £459.

During the English Civil War between the supporters of Charles I and Parliament, Weymouth was predominantly Parliamentarian in loyalty and the surrounding forts were held by their garrisons.
Robert Dormer, the Earl of Carnarvon, entered Dorset with an army in 1643 and Weymouth surrendered, resulting in Sandsfoot Castle being controlled by the Royalists between August 1643 and June 1644.
During this period the castle may have been used as a Royalist mint.
Robert Devereux, the Earl of Essex, then retook the county for Parliament; Colonel William Ashburnham, the Royalist governor of Weymouth, retreated to Portland Castle without a fight.
Devereux approached Sandsfoot and, after three hours of negotiations, the fort surrendered to him.
In 1647, Parliament ordered the garrison at the castle to be demobilised but this did not occur, and John Hayne was appointed as its new captain.

Charles II was restored to the throne in 1660 and the next year a fresh order was given to demobilise the garrison at Sandsfoot.
An argument then broke out between Humphrey Weld, the lieutenant-governor of Portland and captain of Sandsfoot Castle, and Charles Stewart, the Duke of Richmond, over the control of the local defences.
The village of Wyke Regis petitioned Weld in a bid to prevent the demobilisation, concerned that their traditional exemptions from militia service would be revoked by the Duke.
Weld championed their case but was dismissed from his post as lieutenant-governor, and the Duke occupied Sandsfoot with his militia.
Weld appealed to the government and in 1665 a compromise was announced in which Weld would be reappointed to his role as lieutenant-governor, while Sandsfoot would be declared redundant and be demolished.
The order for its destruction was never carried out, and the castle was used as a storehouse until at least 1691.

By 1725, the castle had become ruinous.
Early in the century, the remains of the castle was sold to the town of Weymouth, whose people reused some of the stone to construct their new town bridge.
Local tradition in the 19th century maintained that several houses in Weymouth were also constructed using stone taken from the castle.
In 1825, the carved stone Elizabethan arms of the castle were moved to All Saints Church in Wyke Regis.
Captains continued to be formally appointed, however, and Gabriel Stewart held the post as late as 1795.

The majority of the gun platform collapsed into the sea as the cliffs eroded.
It is uncertain precisely when this occurred; in a prolonged historical debate over this during the late 19th and early 20th centuries, the historian Henry Symonds argued that the first falls occurred during the 18th century, W. Norman placed the main fall in 1835, and T. Groves argued in favour of a more recent collapse in the second half of the 19th century.
The ruined castle was drawn and painted by various artists in the 18th and 19th centuries, including Samuel Buck, J. H. Grimm, C. Sawyer and Edward Pritchard.
The castle featured in Joseph Drew's short novel "the Poisoned Cup" in 1876.
Repairs were made to the castle between 1610 and 1611 by the captain, Sir George Bampfield, at a cost of £211. A survey in 1623 carried out by Sir Richard Morryson showed the castle to be equipped with ten iron guns – one culverin, five demi-culverins, two sakers, a minion and a falcon – and garrisoned by its captain, five gunners and three soldiers. It was in a poor condition, and one corner of the gun platform had been undermined by the sea; Morryson's team estimated the likely costs of repairs to amount to £459.
During the English Civil War between the supporters of Charles I and Parliament, Weymouth was predominantly Parliamentarian in loyalty and the surrounding forts were held by their garrisons. Robert Dormer, the Earl of Carnarvon, entered Dorset with an army in 1643 and Weymouth surrendered, resulting in Sandsfoot Castle being controlled by the Royalists between August 1643 and June 1644. During this period the castle may have been used as a Royalist mint. Robert Devereux, the Earl of Essex, then retook the county for Parliament; Colonel William Ashburnham, the Royalist governor of Weymouth, retreated to Portland Castle without a fight. Devereux approached Sandsfoot and, after three hours of negotiations, the fort surrendered to him. In 1647, Parliament ordered the garrison at the castle to be demobilised but this did not occur, and John Hayne was appointed as its new captain.
Charles II was restored to the throne in 1660 and the next year a fresh order was given to demobilise the garrison at Sandsfoot. An argument then broke out between Humphrey Weld, the lieutenant-governor of Portland and captain of Sandsfoot Castle, and Charles Stewart, the Duke of Richmond, over the control of the local defences. The village of Wyke Regis petitioned Weld in a bid to prevent the demobilisation, concerned that their traditional exemptions from militia service would be revoked by the Duke. Weld championed their case but was dismissed from his post as lieutenant-governor, and the Duke occupied Sandsfoot with his militia. Weld appealed to the government and in 1665 a compromise was announced in which Weld would be reappointed to his role as lieutenant-governor, while Sandsfoot would be declared redundant and be demolished. The order for its destruction was never carried out, and the castle was used as a storehouse until at least 1691.
By 1725, the castle had become ruinous. Early in the century, the remains of the castle was sold to the town of Weymouth, whose people reused some of the stone to construct their new town bridge. Local tradition in the 19th century maintained that several houses in Weymouth were also constructed using stone taken from the castle. In 1825, the carved stone Elizabethan arms of the castle were moved to All Saints Church in Wyke Regis. Captains continued to be formally appointed, however, and Gabriel Stewart held the post as late as 1795.
The majority of the gun platform collapsed into the sea as the cliffs eroded. It is uncertain precisely when this occurred; in a prolonged historical debate over this during the late 19th and early 20th centuries, the historian Henry Symonds argued that the first falls occurred during the 18th century, W. Norman placed the main fall in 1835, and T. Groves argued in favour of a more recent collapse in the second half of the 19th century. The ruined castle was drawn and painted by various artists in the 18th and 19th centuries, including Samuel Buck, J. H. Grimm, C. Sawyer and Edward Pritchard. The castle featured in Joseph Drew's short novel "the Poisoned Cup" in 1876.
Sandsfoot Castle