YSK: How to document that you are a US citizen
https://www.usa.gov/prove-us-citizenship
The most common way to show that you are a US citizen is to show a passport. However, only about 50% of US citizens have a passport.
An alternative to a passport is a Certificate of Citizenship.
Certificates of Citizenship and Naturalization show proof that someone is a U.S. citizen. The website https://www.usa.gov/prove-us-citizenship shows how you can get or replace these documents.
Prove your citizenship: born in the U.S. with no birth certificate. If you were born in the U.S. and have no birth certificate, learn how to get documentation to prove you are a U.S. citizen.
Prove your citizenship: born outside the U.S. to a U.S. citizen parent. Prove your U.S. citizenship without a birth certificate if you were born outside the U.S. to a U.S. citizen.
I did a search on it. You get different numbers. Some sources say 45% to 50%.
Are those numbers for passports only, or do they include “passport cards” which are only good for Canada and Mexico?
Also only good for ground travel. But you have to go through the same process as a passport, so they’re usually an add on to the passport.
Do those not also verify citizenship?
They do. For all intents and purposes they are a passport with severely restricted international travel limitations.