St Asaph is a cathedral city and community on the River Elwy in Denbighshire, Wales. In the 2011 Census it had a population of 3,35…St Asaph is a cathedral city and community on the River Elwy in Denbighshire, Wales. In the 2011 Census it had a population of 3,355, making it the second-smallest city in the United Kingdom in terms of population and urban area. It was historically in Flintshire.