Codnor Castle is a ruined 13th-century castle in Derbyshire, England. The land around Codnor came under the jurisdiction of William Peverel after the Norman conquest. Although registered as a Scheduled Ancient Monument and Grade II Listed Building the site is officially, as at 2016, a Building at Risk.
The castle is a stone keep and bailey fortress and was established by William Peverel. The present fragmentary remains represent a three-storey keep and a strong curtain wall and ditch, flanked by round towers. The outer bailey is on a lower level and was constructed at a later period. The castle overlooks the Erewash valley and the counties of Derbyshire and Nottinghamshire. It originally had a deep moat and on its eastern side there was once a considerable abundance of trees, which have now been cut down. On the west side there was a courtyard that was strongly fortified by huge round towers, which had battlements. In other parts of the ruins there is evidence that the outer walls had arrow-loops included to allow bowmen to use them if necessary.