William III de Ferrers, 5th Earl of Derby of Chartley Castle in Staffordshire, was an English nobleman and major landowner, unable through illness to take much part in national affairs. From his two marriages, he left numerous children who married into noble and royal families of England, France, Scotland and Wales.

Chartley Castle lies in ruins to the north of the village of Stowe-by-Chartley in Staffordshire, between Stafford and Uttoxeter. Mary, Queen of Scots, was imprisoned on the estate in 1585. The remains of the castle and associated earthworks are a Scheduled Monument, the site having been protected since 1925. The castle itself is a Grade II* listed building