This article tells the story of engineering and technology at Castleford Water Mills from the seventeenth century to the twentieth century through the presentation of recently discovered design plans and deeds, supplemented by other historical research. One of Castleford's mills was operated by Dr Thomas Allinson's Natural Food Company and therefore retained stoneground milling when fashions for white flour prompted other mills to switch to roller systems. The millstones were powered by a high-efficiency breastshot wheel, believed to be the last of its type taken out of industrial service in Britain. Many of its features, and its subsequent longevity, can be attributed to the influential works of William Fairbairn and John Smeaton. Detailed colour designs show the construction specifications of this water-wheel and its civil housing, along with other engineering plans such as a previously unrecorded Henry Simon horizontal turbine. Links with John Smeaton and the entry in his catalogue of designs for Castleford Oil Mill are also explored, and a former flood mill is identified at the site.