I think the last time they actual brought someone to trial to fine them was back in the 1970s and the Census specifically went after them because they were publicly announcing on a radio program that they weren't going to fill out their census forms.
Yeah....
The regs have been redone since then but I read them carefully and there is still no stated language of enforcing it, (meaning who would do it, and how)
BTW, they call these things surveys, and not the census counting..
Over time, various agencies have asked and been granted information that supposedly cannot be traced back to a name but that they use for policy formation and other purposes.
One would be right in not trusting the good intentions.