I was told the Department of State has a database of who is and isn't a US Citizen, and there is nothing worry about.
I am sure every department has a database. And I am sure many departments have a list of USCs ... Social Security people for example. How accurate and useful this information is a different question.
The relevant question in this context is ... if you need to prove your identity, what proof will this custodians of database require to help you? Their response
==> I am not authorized to reveal whether "style1983" exists in our DB or not
==> I am not authorized to reveal whether "style1983" is a citizen or not
==> Oh, you are "style1983". Prove it ...
[ADD]
==> I see a style1983 who got a US passport, but I have no clue how he/she became citizen. I will need to send it to someone upstairs.
Having said that, like anything, there is a NORMAL distribution curve of citizens. On one end of the range, some do not even step out of the country. On the other end, they live outside.
On one end of the curve, you can do serial crimes, and never get caught. On the other end of the curve, you can get caught jaywalking when you try it the first time.
The question is a) which end of the spectrum your life puts you in, and b) what protection do you invest in if you happen to land up on the bad side of this NORMAL curve.