Mountain Ash Urban District was a local authority in Mountain Ash, in the Cynon Valley, Glamorgan, Wales. It was created in 1894 as a result of the 1894 Local Government of England and Wales Act.The Council existed until 1973 and replaced the Mountain Ash Local Board of Health which had functioned since the 1870s. Initially, the Council had fifteen members, but this was increased to eighteen in 1898. The council was based at Mountain Ash Town Hall.