Latin, comitatus, scira, scyra.
Counties were the primary structural element of Domesday Book. There were 31 counties in Great Domesday. Each county was divided into fiefs, each fief into Hundreds, each Hundred into vills, and each vill into manors.
Domesday Book is the earliest source which allows us to reconstruct the boundaries of counties, the fundamental units of English government. Broadly speaking, the boundaries of Domesday counties are those that existed until 1974. In southern England, boundary adjustments in the intervening nine centuries have been modest, only the area around London involving significant change as the capital expanded to absorb parts of adjacent counties. In the north, there was more uncertainty. The areas which would develop into the counties of Cumberland, Lancashire and Westmoreland were appended to Yorkshire and Cheshire as Craven, Amounderness and the land between the Ribble and the Mersey in 1086. Rutland was intermingled with several counties; and small sections of Derby and Nottingham and Yorkshire and Lincolnshire were also intertwined.
Details of boundary adjustments between 1086 and 1974 are described in the 5 regional volumes of the monumental Domesday geographies edited by H.C. Darby and others: Domesday geography of Eastern England (third edition, 1971); Domesday geography of Midland England (second edition, 1971); Domesday geography of South-East England (1962); Domesday geography of Northern England (1962); and Domesday geography of South-West England (1967).