Grosmont (Welsh: Y Grysmwnt or Rhosllwyn) is a village and community near Abergavenny in Monmouthshire, Wales. The population taken at the 2011 census was 920. The wider community (parish) includes the villages of , Llangua and Llanvetherine.
There are circumstantial indications (Pickford, 2003) that Grosmont may have originated as an Iron Age camp. Grosmont Castle is a major feature of the village and was the birthplace of Henry, 1st Duke of Lancaster. Grosmont was once an important medieval township. It was granted a borough charter, possibly in 1219, and by 1250 there may have been as many as 160 burgage plots. It retained its corporation status until 1857, at which time it still had a mayor and an official ale taster. The town hall replaced a former timber structure and was built in 1832 by the then landowner the 6th Duke of Beaufort, whose descendant offered it to the Grosmont Parish Council in May 1902. A market used to be held twice a week.
The Church of St Nicholas probably has ancient origins but the tower and other parts were built by Prince Edmund (son of Henry III of England and later Edmund Crouchback, 1st Earl of Lancaster) for his mother Eleanor of Provence (Queen Eleanor).The 14th century church is dedicated to St Nicholas and was restored by J. P. Seddon in 1869. It has an unusual eight-sided tower.