Previously the railway existed in a much smaller form around a disused pumping station in Farnham, and was then known as the Wey Valley Light Railway. This had originally been founded in the early 1970s using narrow gauge railway equipment from local industrial lines. When the Wey Valley site was acquired for redevelopment in 1982 the railway was moved lock, stock and barrel to form the nucleus of the Old Kiln Light Railway and has now very much outgrown its humble beginnings. The railway is wholly independent of the main museum. It is run, owned and funded by a small group of enthusiasts and is entirely self financing.
Income comes from the individual members and from train fares and public donations.
The railway runs on Sundays throughout the summer and on occasional Saturdays and bank holidays. There is currently approximately a quarter mile of running track together with associated sidings, workshops and sheds. Rolling stock consists of various forms of motive power including both steam and internal combustion locomotives. Restoration of both is undertaken on and off site, and there is always work going on in the busy workshops. Passengers are catered for in replica examples of rolling stock used on Welsh narrow gauge lines.