The Annales Londonienses record that "Ranulphus comes Cestriæ" had four sisters, of whom "tertia…Agnes" married "comiti de Ferrariis, id est Derby, Willelmo seniori".
Lady of Chartley, Staffordshire, and Bugbrooke, Northamptonshire, following her brother's death in 1232.
The Annals of Burton record the death “X Kal Oct” in 1247 of “Willelmus de Ferrariis…comes Derbeiæ” and “IV Non Nov” of “Agnes comitissa uxor eius”. 1
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17 May 1249, Reading
The king has granted to W. de Ferrers, formerly earl of Derby, that his heirs may answer the king for all debts in which he was bound to him, both for his own debts and the debts of others. Order to the barons of the Exchequer to cause no distraint to be made upon the executors of his testament or upon the executors of Agnes, formerly countess of Derby, his wife, for the aforesaid debts. If they have done anything towards them, they are to remit it.
Calendar of Fine Rolls, 33 Hen. III, 221
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