Penda son of Pybba ruled from about 626 or 633 until 655. Some of what is known about Penda comes through the lengthy account given by Bede, who condemned Penda both for being an enemy to Northumbria and for being a pagan, though Bede admits that Penda freely allowed Christian missionaries from Lindisfarne into Mercia, and did not restrain them from preaching. Penda ruled at a time of changes in the balance of power between the kingdoms of Britain and in the influence of Christianity.

A separate political existence from Wessex was briefly restored in 955–959, when Edgar in rebellion against his brother became king of the Mercians, and again in 1016, when the Kingdom of the English was divided between Cnut and Edmund Ironside, Cnut taking Mercia and Northumbria.The West Mercia Constabulary was created in 1967, combining the police forces of Herefordshire, Shropshire and Worcestershire. All the following are kings, unless specified. Those in italics are probably legendary, are of dubious authenticity, or may not have reigned. Bateman, John (1971). The Great Landowners of Great Britain and Ireland. Leicester University Press. ISBN 0-391-00157-4. At the end of the 9th century, following the invasions of the Vikings and their Great Heathen Army, Danelaw absorbed much of the former Mercian territory. Danelaw at its height included London, all of East Anglia and most of the North of England.

Bradbury, Jim (2004). The Routledge Companion to Medieval Warfare. Routledge. p.137. ISBN 978-0415221269. Margaret Gelling. 'The Early History of Western Mercia'. (p.184–201; In: The Origins of the Anglo-Saxon Kingdoms. S. Bassett. 1989)Stenton, F. M. (1970). "The Supremacy of the Mercian kings". In Stenton, D. M. (ed.). Preparatory to Anglo-Saxon England. Oxford. pp.48–66. {{ cite encyclopedia}}: CS1 maint: location missing publisher ( link) King Peada converted to Christianity around 656, the Diocese of Mercia was founded in this year, with the first bishop ( Diuma) based at Repton. The religion was firmly established in the kingdom by the late 7th century. After 13 years at Repton, 669 AD, Saint Chad (the fifth bishop) moved the bishopric to Lichfield and, in 691 AD, the Diocese of Mercia became the Diocese of Lichfield. There has been a diocese based in the city ever since. For a brief period between 787 and 799 or 803 the diocese was an archbishopric. The current bishop, Michael Ipgrave, is the 99th since the diocese was established. Foot, Sarah (2011). "Æthelstan (Athelstan) (893/4–939), king of England". Oxford Dictionary of National Biography. Oxford University Press. doi: 10.1093/ref:odnb/833 . Retrieved 28 August 2021. After Mercia was annexed by Wessex in the early 10th century, the West Saxon rulers divided it into shires modelled after their own system, cutting across traditional Mercian divisions. These shires survived mostly intact until 1974, and even today still largely follow their original boundaries.