The Grand Jury, before its abolition in 1933, were charged with determining if there was sufficient evidence in a case to warrant its going to trial. Its members, chosen from among the local gentry, would meet in this room, hear evidence from witnesses under oath and then decide if there was a case to be answered.

The table and chairs are Gillow, as is the witness stand,and they make up the castle's finest examples of that firm''s craft. Each chair displays a face on the apex of its back, and these represent many different people, from old men to cherubs, while a great number also represent different types of animals: lions and monkeys, and even a snake. The throne-like chair by the door is also Gillow and was made for the visit of Queen Victoria to the castle in 1851.

Like the Drop Room below it, the Grand Jury Room is a perfect circle, with doors bowed to fit the curvature of the walls and a beautiful plaster ceiling painted to look like stone.