Mercian was spoken in the Anglo-Saxon kingdom of Mercia. It was one of four distinct dialects of Old English, the other three were Kentish, Northumbrian and West Saxon.

The dialect was spoken from East Anglia through the midlands to the Welsh border, with the Northumbrian dialect to the north and the West Saxon dialect to the south. During the Viking invasions of the 9th century, Northumbrian came under the influence from the languages of the Viking invaders.