This is an English locational surname of great antiquity. It does originate from the town of Sydenham in Kent. The dictionary of English surnames claims that Sydenham and Chippenham have exactly the same meaning, but seems to be uncertain what that is! We do know though that Sydenham is the "Norman" pronunciation. Locational surnames are usually "from" names. That is to say surnames given to people after they left their original homes to move somewhere else, as an easy means of identifying strangers. A good example ois the surname Hampshire, which is probably most popular far away in Yorkshire. In the case of Sydenham much the same applies. The first recording being that of John de Sydenham, in the county of Somerset in 1272, whilst Simon de Sidenham who could even have been John's brother in rolls of the following year. In the marriage licences of the year 1586 we have the more unusual recording of Roger Raston who married Sybil Sydnam in the city of London, whilst Himphrey Sydenahm married a widow Elizabeth St John at Canterbury Cathedral in 1674.