Why?
If you’re in the US, you should know this because if you want to apply for a passport, you’ll be required to provide information about your parents such as birth dates and places. If you’re divorced, you will have to provide the same info along with marriage and divorce date, even if it was decades ago. So if you have access to that info, make sure you record it somewhere safe for Future use.
If you’re not in the US, you should know because this information can be difficult for people to get if they never knew one or both parents, or have a bad/non-relationship with them. Or if they had a contentious divorce or an abusive partner. Which is another reason why just leaving the country can be difficult for people who are already marginalized.


Isn’t this due to the US not having a working census database?
Please correct me if I am wrong.
From what I have heard, you need to bring bills with your address to prove where you live in some circumstances in the US.
Here in Sweden, or any sane country, I simply use my personal number to identify myself, and bam, the requesting entity can find the info they need.
As an American/Swedish dual citizen…
I think I’ve only had to show mail to prove my address when first getting a driver license in a new state. So that’s a thing yes, but not very common.
Unlike in Sweden, in the US you don’t register/update your address with the authorities when you move. It’s not that the US doesn’t have a “working database” for that – it’s just not a thing at all, there’s no population register like in Sweden.
In Sweden you use your personnummer for identification, but you also have secure authentication methods like BankID that aren’t available in the US. Your personnummer is public information and you’ll provide it just about everywhere because there’s little risk to you.
In the US we use our social security numbers for both identification and authentication. Because they’re used for authentication, they’re considered secret and we’ll only share them when strictly required for necessary services (like government agencies and banks). This is obviously really poor security and they weren’t originally intended to be used for authentication, but it is what it is.
Swedish system is of course more efficient and more secure.
I have to show my water bill to dump my monthly free truckload at the landfill, but that’s about it. Sometimes utilities require it too.
Thank you for clarifying this!
The US badly needs a population database, however, I absolutely understand that with how the US government have abused and fooled their citizens in the past, there is a huge distrust of the government among Americans.
Yeah people won’t even fill out the census. Last time it was done most of the people I worked with said they wouldn’t fill it out.
The US government has the information, but there’s no way for companies to sell you something if they used that data.
It’s the same with US taxes. The IRS knows exactly how much you owe them each year. As a citizen, you cannot access that information. You have to fill out needlessly complicated forms to guess the correct amount of money to send them. If you guess wrong you can go to jail or be fined. To prevent this, you pay a company to fill out those forms. They don’t get access to the correct number either, but you can buy insurance from them so they’ll pay for your lawyer to defend you if you guess wrong.
Kind of
The vast majority of the time we use our social security numbers as a personal ID number. Drivers licenses also will have unique numbers on them which you can query off of, so too do passports.
By law, no one is required to have any of those three. People having a social security number is pretty common, but getting one of those is the easiest of the three.
Because none of them are a legal requirement to be a citizen, each one has multiple document set requirements, and if you have the other two, the third is trivial to obtain.
The documents you need if you’re not leveraging another form of ID are basically a set of documents that aren’t that difficult for your average person to get their own copies of but harder for some one else to forge and claim to be another person