Under privacy laws, the records could only be publicly released after 100 years.
They list crucial details such as the name, age, residence and profession of all 38 million people living in England and Wales at the time.
Tamsin Todd, CEO of Findmypast, said: “This is a day when we as a nation get to reflect on our shared history and personal history, as we read the extraordinary stories captured by the 1921 Census of England & Wales.
“Taken between two world wars, following a global flu pandemic, during a period of economic turmoil and migration, with social change at home as women won the right to vote, the 1921 Census documents a moment in time that will resonate with people living today.
“It has been a great honour for Findmypast to work with The National Archives as its selected partner to digitise and transcribe the 1921 Census.”
Family historians shared their excitement on social media as they added a new chapter to their family story by locating their relatives in 1921.
My first discovery is my grandad, George Willoughby (on the horse!) who was 20 years old and living in his home village of Hilcott, Wiltshire. The census gives the name of the farm where he worked as a labourer. He is living with his mum but his sisters are missing…#1921Census pic.twitter.com/BIJuOGXs5L
— Angela Buckley ???? (@victoriansleuth) January 6, 2022
First two #1921Census downloads completed. My great-grandparents in Newport, each still living with their parents (bonus!) George is an engine cleaner for GWR at Maesglas Sheds. Rose’s father’s handwriting is awful! Through no fault of the transcriber she’s indexed as ‘Fisca’.
— Jenni Phillips (@JenniPh) January 6, 2022
Interesting to see my 2x great grandmother on the 1921 census. My 2x great grandfather died in an accident so she remarried. The second marriage was a disaster and he disowned her publicly, 1890s. She used first husband’s name on 1901 and 1911 but second husband’s on #1921Census
— Miss Jean A O’Logie (@JeanAOLogie) January 6, 2022
The 1921 census captures greater detail than any previous census record.
For the first time, entrants were required to put their age in years and months, not just years, and were asked the name of their employer and their place of work.
Records for children state whether the child had both parents alive, one parent alive or both parents dead, and records for adults provide the opportunity to state whether they’re divorced as well as single, married or widowed.
Many famous Britons can be found in the records.
Pioneering film director Alfred Hitchcock is listed, age 21 years and 10 months, living in Southwark, London with his mother Emma.
He is working in his first role in the film industry, as a title designer for Famous Players-Lasky.
Beloved children’s author Beatrix Potter appears under her married name of Helen Beatrix Heelis, living at Ulverston in the Lake District.
She was a keen sheep farmer as well as an author.
Her profession is given as ‘Farmer’ and her place of work as Sawrey, where she kept her farm.
National hero Captain Sir Tom Moore, who was knighted for his fundraising efforts during the covid-19 pandemic, can also be found in the census, aged just one year and one month.
He is living in Keighley, Yorkshire with his father Wilfred, mother Isabel, and older sister Freda.
The 1921 census results also reveal the impact of the First World War, which ended three years previously.
So many men were killed in the war that there was a gender disparity of 1,096 women recorded for every 1,000 men, and 730,000 children recorded with a dead father versus 261,000 with a dead mother.
There was also a 35% increase in the number of people recorded in hospital compared to the 1911 census, reflecting the number of injured war veterans.
Access to the 1921 census records for England and Wales is not covered as part of a Findmypast subscription.
The records are available at a cost of £2.50 for every record transcript and £3.50 for every individual image, with a 10% discount for Findmypast’s Pro subscribers.
They are also free to view at access hubs in The National Archives in London, the National Library of Wales in Aberystwyth and Manchester Central Library.
The release of the 1921 census for Scotland has been delayed.
It will be available on Scottish records website ScotlandsPeople in the latter half of this year.
There is no 1921 census for modern-day Northern Ireland as Ireland was caught up in the Irish War of Independence at the time.
Rosemary Collins is the Who Do You Think You Are? Magazine features editor