Montgomeryshire/ Sir Drefaldwyn Montgomeryshire, also known as Maldwyn is one of thirteen historic counties and a former administrative county of Wales. It is named after one of William the Conqueror's main counselors, Roger de Montgomerie, who was the 1st Earl of Shrewsbury. Montgomeryshire constitutes the northern part of the principal area of Powys, according to the 2001 census its population was 59,474