Orig. a sphere of jurisdiction or command; thus the area over which such authority was exercised. The earliest shires (in Wessex) were commanded by ealdormen; by the late 10c, when the ealdorman's powers were more extensive, they were administered by sheriffs. By the same period, the shires were divided into hundreds (in the north, wapentakes). From the 12c, they were also called 'counties'. Latin form is scira. [< OldEngl. scir = division, sphere of control, shire]
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.