Westerham is a town and civil parish in the Sevenoaks District of Kent. It is located on the border of Kent with Greater London and Surrey, bordering Bromley and the Tandridge District. It is located west of Sevenoaks.It is recorded as early as the 9th century, and was mentioned in the Domesday Book in a Norman form, Oistreham (compare Ouistreham in Normandy, Oistreham in 1086).Hām is Old English for a village or homestead, and so Westerham means a westerly homestead.