Domesday Book (/ˈduːmzdeɪ/ or /ˈdoʊmzdeɪ/), now held at The National Archives, Kew, in South West London, is the record of the great survey of much of England and parts of Wales completed in 1086. The survey was executed for William I of England (William the Conqueror): "While spending the Christmas time of 1085 in Gloucester, William had deep speech with his counsellors and sent men all over England to each shire to find out what or how much each landholder had in land and livestock, and what it was worth" (Anglo-Saxon Chronicle).
Among other areas it does not cover is London.
More information on the Wikipedia page [1]. The National Archives pages are [2] and [3]. The Domesday Book Online website is here and the Open Domesday website is here.