Not that these people would ever pay it.
The only question a person is legally required to answer is the amount of people in the household. The rest of the questions are like someone else posted, NOYFB. If you only answer that one question, you can look forward to someone from the census board calling you and TELLING you, you HAVE to answer all questions or you will be fined and possibly spend some time in jail. But no matter what they say, you can tell them to stick it.
“The Census Act (13, U.S.C., §221) requires responses to the decennial census. A person who “refuses” or “willfully neglects” to answer any census questions is subject to a fine of not more than $100. A person who “willfully” provides false information can be fined up to $500 (§222). The 2010 census questionnaire covers six topics: age; gender; relationship to head of household; Hispanic origin; race; and tenure (homeowner or renter). The Census Bureau requests names of people residing in the household, to ensure full coverage and minimize the likelihood of duplication, and a telephone number, in case it must follow-up to obtain missing or unclear information, but it does not ask for social security or any other identification number.”
Notice the special inquiry into *Hispanic* origin.