Today marks the creation of five new councils, including two new unitaries and three districts.
The two new unitary councils established in Dorset to replace nine local authorities were approved by Parliament in May last year.
Dorset Council has been established to replace Dorset CC, North Dorset, East Dorset, West Dorset and Purbeck DCs and Weymouth and Portland BC.
The council will have 8,000 staff, including those in education, serving a population of 375,000.
Dorset chief executive Matt Prosser said creating a new unitary council in the short amount of time available had been a challenge but he was “delighted with our progress”.
He added: “It has not been an easy process and we’re having to make some difficult decisions, but everyone has really pulled together to make this happen. We hope that residents will see little or no change to services on day one.”
Bournemouth, Christchurch and Poole Council replaces Bournemouth and Christchurch BCs and Borough of Poole Council.
Graham Farrant was appointed chief executive of the council in in October last year. He has previously been chief executive of Thurrock Council and Barking & Dagenham LBC.
The new council will serve a population of 400,000.
East Suffolk Council replaces Suffolk Coastal and Waveney DCs to create the largest district council in the country with a population of 250,000.
Suffolk Coastal and Waveney have worked in close partnership for 11 years and have had an integrated workforce since 2010.
Chief executive Stephen Baker said it is “a momentous day”.
He added: “On the one hand we have now introduced a major change to local government structure that has never before been achieved in this way, and yet it will very much be business as usual.
“We will continue to work and deliver services much as we have been doing - carefully, diligently, efficiently, united around our shared values.”
Forest Heath DC and St Edmundsbury have today been replaced by West Suffolk Council after sharing staff and services for many years.
Somerset West and Taunton Council has replaced West Somerset DC and Taunton Deane BC.
Both mergers were approved in May last year.
Elections at the new councils will take place on May 2.