Note that the Census is supposed to be an 'enumeration' (count) of the people in the U.S., not a count of citizens.

"Supreme Court hears arguments over citizenship question on census" PBS NewsHour 4/23/2019

"Why census experts fear a citizenship question would jeopardize results" PBS NewsHour 4/23/2019

Excerpt

SUMMARY:  Counting the roughly 327 million people currently living in the U.S. is a massive effort.  And this year, before the next census moves forward, the Supreme Court must decide whether the Trump administration should be allowed to add a citizenship question to it, over the concerns of census experts.  Judy Woodruff talks to the National Law Journal’s Marcia Coyle and NPR’s Hansi Lo Wang for analysis.