I have just been talking to my oldest friend, who comes from Derby, as I do. He was a little annoyed, because he had seen a television programme about Kedleston Hall, which is in the Amber Valley to the northwest of Derby. His annoyance was caused by the pronunciation of the name in the programme. Anyone in Derby and the surrounding areas will tell you that it is [ˈkedləstən] and NOT [ˈkedlstən], which was the pronunciation used in the programme. I am sorry to say that the 2nd edition of the BBC Pronouncing Dictionary of British Names also gives the latter pronunciation. Wikipedia gets it right however and even has a sound file, presumably of a local speaker, saying the name.
The Concise Oxford Dictionary of English Place-Names, 4th Edition (Ekwall, 1964) gives the derivation as Ketel’s tūn, the homestead belonging to Ketel. The name is from Old Norse Ketill
Some other Derbyshire place-names which catch people out in the same way are Ilkeston, which is [ˈɪlkəstən] and not [ˈɪlkstən] and Chaddesden [ˈtʃædəzdən] and not [ˈtʃædzdən]. My BBC dictionary has both of these correct. The former name has an alternative traditional spelling and pronunciation: Ilson [ˈɪlsən]. Just to show the problems “outsiders” face — Swarkestone is [ˈswɔːkstən].
Another pronunciation that is likely to get you a funny look in Derby and those parts is [ˈbɒrəʊæʃ] for Borrowash. It should be [ˈbɒrəwɒʃ]. So there!