Stephen W Williams or Stephen Williams (1837–1899) was a civil engineer and architect who worked mainly in Radnorshire and Breconshire, Wales. He was county surveyor of Radnorshire from 1864 to 1899. He had offices at Rhayader and lived at Penralley House, Rhayader, He became a noted authority on the archaeology of the Cistercian Monasteries in Wales and undertook excavations at Strata Florida Abbey in Ceredigion, Abbey Cwm Hir in Radnorshire and Strata Marcella near Welshpool in Montgomeryshire. He was appointed High Sheriff of Radnorshire in 1899.