The Black Country is a region of the West Midlands in England, west of Birmingham, and commonly refers to all or part of the four Metropolitan Boroughs of Dudley, Sandwell, Walsall and Wolverhampton.
During the Industrial Revolution, it became one of the most industrialised parts of Britain with coal mines, coking, iron foundries, glass factories, brickworks and steel mills producing a high level of air pollution.
Upd: Carol Thompson the curator "The Making of Mordor" at Wolverhampton Art Gallery in the last quarter of 2014 stated that J. R. R. Tolkien's description of the grim region of Mordor "resonates strongly with contemporary accounts of the Black Country", in his famed novel The Lord of the Rings. Indeed, in the Elvish Sindarin language, Mor-Dor means Dark (or Black) Land.
It is also claimed by one Black Country scholar (Peter Higginson) that the character of Bilbo Baggins may have been based on Tolkien's observation of Mayor Ben Bilboe of Bilston in The Black Country, who was a Communist and Labour Party member from the Lunt in Bilston. But the scholarly evidence for this is still questionable. (Ibid.)