Refusal to answer census questions is covered under 13 USC Sec 221, providing for a fine of no more than 100.00; that acknowledged, can a person elect to refuse to answer a specific question because he believes it may tend to incriminate?
Background: The 2020 US census is proposing to ask 'Are you a US Citizen? In and of itself that might be considered to be a innocent question, but given the political climate a respondent could easily assume that the information is being gathered (or shared with) the Justice Department and/or Immigration Control for the purpose of identifying and locating non-documented residents.
Regardless of an assertion that census data is not supposed to be used in a legal proceeding against the respondent, that respondent has no reason to believe that his answer would never used in that fashion.... consequently his conviction that the information MAY used against him.
IANAL, so .... thoughts