Llanychlwydog 1 stands to the south-west of the former St David's Church, Llanychlwydog (NPRN 308784). It was first noted in 1883, and is thought to have been found during the 1864 demolition of the church and erected on the building's south side. Excavations within the churchyard in the 1984-1985 revealed a number of cist graves, one of which was radiocarbon dated to 890+60 AD. The stone would almost certainly have functioned as an upright grave marker within the early medieval cemetery excavated within the churchyard. It is one of four early medieval stones found within the churchyard.

It is an incomplete cross-carved stone of spotted dolerite. Measurements are given as 90cm height x width 47cm max. x diameter 10 < 12cm. The stone is carved with a cross on both faces. At the top of face A is a linear Latin ring-cross, and the top of face B is a linear cross. Both carvings are thought to date to the seventh to ninth century.

Sources include:
Edwards, N. 2007, Corpus of Early Medieval Inscribed Stones and Stone Sculpture in Wales

N Vousden, 19 October 2018