Latin, Inter Ripam et Mersham.
In 1086, Lancashire had yet to achieve the status of a county, a status it achieved early in the twelfth century. In Domesday Book South Lancashire was described as an appendage to the county of Cheshire under the description of Land between the Ribble and the Mersey.
Like North Lancashire, the southern part of the future county was, or had been, under the control of a single Norman tenant-in-chief, Roger of Poitou, and was only sketchily described in Domesday. According to this account, South Lancashire was sparsely populated by a mere 260 peasant families in 1086, and its manorial value had declined by 70%, possibly as a result of the Conqueror's 'harrying of the north' in 1069-70, though some historians believe that the apparent desolation of the area is due more to defects in the Domesday record than to the ravaging of Norman armies.
For more detail on the area, see Denise Kenyon, The origins of Lancashire (1991); and M.A. Atkin, 'The "Land between Ribble and Mersey" in the early tenth century', Names, places and people: an onomastic miscellany for John McNeal Dodgson, edited by Alexander R. Rumble and A.D. Mills (1997), pages 8-18; and for the debate on the 'harrying', see R. Welldon Finn, The Norman Conquest and its effects on the economy, 1066-1086 (1971); D.M. Palliser, 'Domesday Book and the harrying of the north', Northern History, vol. 29 (1993), pages 1-23; and John J.N. Palmer, 'War and Domesday waste', in Armies, chivalry and warfare in medieval Britain and France, edited by Matthew Strickland (1998), pages 256-78.