County Durham, or officially Durham, is a non-metropolitan county of historic origin in North East England. Ceremonially the county consists of ten districts, three of which are unitary authority areas. Though no Act of Parliament has ever named any entity "County Durham" (the term rising out of common usage), they have changed the boundaries over time. The form of the county name is unique in England. Many counties are named after their principal town, and the expected form here would be Durhamshire.[citation needed] The reason it is called County Durham is that Durham did not become a county until after the language of government was changed from Anglo-Saxon to Norman French in 1066.[citation needed] Previous to that it was a semi-independent Bishopric.[citation needed]