Montgomeryshire (Welsh: Sir Drefaldwyn 'the shire of Baldwin's town', or simply Maldwyn) was one of the thirteen counties of Wales that existed from 1536 until their abolition in 1974, later becoming a district of Powys from 1974 to 1996. It was named after its county town, Montgomery, which in turn was named after one of William the Conqueror's main counsellors, Roger de Montgomerie, who was the 1st Earl of Shrewsbury.
The area of what was Montgomeryshire, now constitutes the northern part of the county of Powys. The current area was 2,174 square km (839 square miles).