Information source: Wikipedia: Counties of England

1890-1965:

• Yorkshire split into Ridings
• Lincolnshire split into Parts
• Sussex split into E & W
• Suffolk split into E & W
• Northants split into Northants and Soke of Peterborough
• Cambs split into Cambs and Isle of Ely
• Hants split into Hants and IOW

1965-1974:

• County of London expanded to Greater London
• Middlesex swallowed mainly by Greater London, but also partly by Surrey and Herts
• Soke of Peterborough and Huntingdonshire merged into Huntingdon and Peterborough
• Isle of Ely merged into Cambs

1974-1995:

• Merseyside - based around Liverpool, south-west Lancashire, along with, from the other side of the River Mersey, the Wirral in north-west Cheshire
• Greater Manchester - the Manchester urban area along with many surrounding towns
• South Yorkshire - based upon the Sheffield-Rotherham area in the West Riding of Yorkshire
• Tyne and Wear - the Tyneside conurbation based on Newcastle-upon-Tyne in Northumberland, along with Sunderland in County Durham
• West Midlands - Birmingham conurbation, including the Black Country and Coventry
• West Yorkshire - Leeds-Bradford area in the West Riding

• Avon formed from northern Somerset, southern Gloucestershire, and Bristol and Bath
• Cleveland formed from southern Durham and northern part of the North Riding, focusing on the Teesside conurbation along with Guisborough and Hartlepool
• Cumbria was formed from Westmorland, Cumberland and part of Lancashire and Yorkshire
• Herefordshire and Worcestershire were merged into Hereford and Worcester
• Humberside formed from eastern Yorkshire and northern Lincolnshire
• Huntingdon and Peterborough was annexed by Cambridgeshire
• Rutland was merged into Leicestershire as a district
• Vale of White Horse, including Berkshire's former county town Abingdon was ceded to Oxfordshire

1995:

• Unitary Authorities start to replace two-tier structures
• Avon, Humberside and Cleveland abolished in 1996
• Rutland becomes separate UA in 1997
• Hereford & Worcester split in 1998 back into Herefordshire UA and Worcestershire county
• Berkshire split into six unitary authorities in 1998, but not formally abolished
• Cheshire and Bedfordshire each split into two unitary authorities in 2009

Information source: Wikipedia: Counties of Wales

1889-1974:

• 13 original counties

1974-1996:

• Replaced by 8 two-tier authorities

1996:

• Unitary Authorities introduced

Information source: Wikipedia: Counties of Scotland, Wikipedia: Subdivisions of Scotland

1889:

• Ross-shire and Cromartyshire merged into Ross and Cromarty

1890-1975:

• 33 original counties (incl. Orkney and Shetland)

1975-1996:

• Replaced by 12 regions (incl. Orkney and Shetland)

1996:

• Replaced by 32 Council Areas (Unitary Authorities)

26 local government districts of Northern Ireland that came into existence in the 1970s, together with four City Councils in the Republic of Ireland and three new counties that emerged from the historic 'Dublin'.  In 2014 Limerick City and North Tipperary will no longer exist and their tops have not been included.