Such records are not kept.
Since records were not kept in this time in history it is hard to give the number of people. Official census records, birth records, and death records were not kept. Most people didn't know when they were born. We do know by an estimate of the amount mass graves that 3/4 of Europe died.
In the US, census records for 1940 and later are subject to privacy laws and are not generally available until they become 72 years old. Earlier Census records are on microfilm and available through local libraries, through the Family History Centers operated by the Mormon Church, and through the US National Archives and its regional branches. The Census records of other countries are available under different circumstances, often only after they are 100 years old.
Marture census records1920 US Federal Census records
You can check the U.S. Census Bureau on an old census about the time they lived there. Get with the local Historical Society for assistance. Birth and death records may also get you there.
There is a company called the National Archives and Records Administration (NARA) that is responsible for making all census records available to the public.
US Federal Census records are not released to the public until 72 years after the census. The most recent Census available to the public is the 1940 census. The 1950 Census will be available in 2022. It is, however, possible to obtain a copy of your owncensus record for certain legal purposes.Most other countries hold their census records as private data for 100 years, and some now hold those records forever private.
No one knows. There have been no records kept.
Use old newspapers, archival records, and census and birth, marriage and death records to find out what you can about a relative whom no one will talk about.
Census records are among the most useful source of data for family historians. Census records can provide genealogical missing link to tie together a group of family members in a way not possible with any other single data source.
The 1950 census records will be released by the National Archives in April 2022. There is a 72-Year Rule that requires that census records not be released to the public until 72 years have passed.
One can find census records for the United States on a few different websites. Some of the sites are the United States Census Bureau and Family Search.