The constitutional requirement for the Census is found in Article. I. Section. 2. Paragraph. 3. “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.”
The purpose of the Census is that of counting the US population in order to apportion among the states the number of representatives in the US House of Representatives. That’s it. Nothing more. Nothing less.
There is nothing in the Constitution requiring or even suggesting questions regarding race, ethnicity, whether one owns or rents his or her home, income status, disability status, education, or anything of the sort. The only purpose of the Census is to count the US population. Anything beyond that is nothing more than an intrusive government prying and snooping into our lives: something the federal government is doing with greater and greater frequency and intensity these days.
As to the phrase, “[As] they shall by Law direct,” Paul Galvin rightly notes, “This language merely goes to the mechanics of the counting (who will do it; when it is to be done; how, when results are to be reported; and so forth); it does not enlarge what may be counted. Constitutionally the only permitted enumeration is the number of people in the United States. Why? Because that count is the determinant for apportionment and therefore the only pertinent information needed.”