The county was formed by the uniting of the shires of Ross-shire and Cromartyshire. Both these shires had themselves been formed from the historic province of Ross, out of which the many enclaves and exclaves that formed Cromartyshire were carved out, leaving the remaining area to become Ross-shire. These parcels of land were for many purposes administered as part of Ross-shire rather than Cromartyshire. The county also included the Isle of Lewis, however this is not part of the modern lieutenancy area (which instead includes the Isle of Skye), although Lewis is part of the current registration county.