The census collects information on everyone because that's what the Constitution says it has to do. There's a bit over 200 years of case law arguing the specifi

The census collects information on everyone because that's what the Constitution says it has to do. There's a bit over 200 years of case law arguing the specifics (e.g. how to handle the "Indians not taxed" exception), but in modern times it's interpreted to mean literally everyone.