The Constitution specifies the purpose of the Census:

Representatives and direct taxes shall be apportioned among the several states which may be included within this union, according to their respective numbers, which shall be determined by adding to the whole number of free persons, including those bound to service for a term of years, and excluding Indians not taxed, three fifths of all other Persons. The actual Enumeration shall be made within three years after the first meeting of the Congress of the United States, and within every subsequent term of ten years, in such manner as they shall by law direct.

That's it.

Enumeration.

Not 'How many bathrooms do you have?"

If they can find a right to privacy that allows the slaughter of innocent children in the womb, you'd think we might be able to avoid answering intrusive questions from the government without fear of prosecution.