Fort Grierson was a secondary fortified outpost located about half a mile (0.8 km) from Fort Cornwallis. This fort was defended by about 80 men under Colonel Grierson. On May 23 the Patriot forces began to encircle the fort in a manner intended to draw Grierson out in an attempt to reach Fort Cornwallis. Brown, aware of the danger to Grierson, sallied forth from Cornwallis, but when faced with Lee's strength, limited his support attempt to an ineffective cannonade.
Grierson, desperate to escape the trap, attempted to flee along the riverbank but his entire company was captured. Clerke's men then took their revenge on similar actions perpetrated by Brown, and refused quarter, killing Grierson and all of his men.