Radnorshire ( Welsh: Sir Faesyfed ) is one of the thirteen traditional counties and a former administrative county of Wales. Historical capital and the eponymous town is the city of New Radnor. Since 1974 Radnorshire is a part of Powys.
The county is bordered by Montgomeryshire, Shropshire, Herefordshire, Brecknockshire and Cardiganshire. The landscape is mountainous and is dominated by the Cambrian Mountains. The highest elevation of 660 m is in the Radnor Forest.
1961 the county had 18,431 inhabitants in 1219 km ².
Until 1974 Radnorshire was an independent administrative county and then next Brecknockshire and Montgomeryshire one of the three districts of the new county of Powys. 1996, all districts were dissolved and Powys has been a unitary authority with the status of a County. At the 2001 census, the area of the former District Radnorshire had 24,805 inhabitants.