Radnor or Radnorshire is one of thirteen historic and former administrative counties of Wales. It is represented by the Radnorshire area of Powys, which according to the 2001 census, had a population of 24,805. The historic county is bounded to the north by Montgomeryshire and Shropshire, to the east by Herefordshire, to the south by Brecknockshire and to the west by Cardiganshire.
The county was formed from the cantrefs of Maelienydd and Elfael and the commotes of Gwrtheyrnion and Deuddwr (the area formerly known as Rhwng Gwy a Hafren) by the Laws in Wales Acts 1535-1542. New Radnor was the original county town, although the Assizes sat at Presteigne and ultimately the County Council formed in 1889 met at Presteigne as well. Some administrative functions, and later the District Council, were based at the larger and more central Llandrindod Wells.
The administrative county formed under the Local Government Act 1888 was abolished by the Local Government Act 1972 in 1974, with its area being transferred to the newly created county of Powys. Powys was divided into three districts, one of which (Radnor) was coterminous with Radnorshire. The district was renamed Radnorshire in 1989. Since Powys became a unitary authority in 1996, Radnorshire has been one of three areas formed under a decentralisation scheme. A "shire committee" consisting of councillors elected for electoral divisions within the former district of Radnorshire exercises functions delegated by Powys County Council.