Cromartyshire is a historic county in the Highlands of Scotland, comprising the medieval "old shire" around the county town of Cromarty and 22 enclaves and exclaves transferred from Ross-shire in the late 17th century. The largest part, six times the size of the old shire, is Coigach, northwest from Ullapool. In 1890, Cromartyshire was merged with Ross-shire into the administrative county of Ross and Cromarty, which in 1975 was merged into the new council area of Highland.

The shires of Scotland, or counties of Scotland, are historic subdivisions of Scotland established in the Middle Ages and used as administrative divisions until 1975. Originally established for judicial purposes, from the 17th century they started to be used for local administration purposes as well. The areas used for judicial functions (sheriffdoms) came to diverge from the shires, which ceased to be used for local government purposes after 1975 under the Local Government (Scotland) Act 1973.