Legal Question in Constitutional Law in Wisconsin

Yes. American law imposes very few duties on us, but answering the census is one of them. Failure to do so is punishable by fines of up to $5,000 (though relatively few such cases are prosecuted, and even then the fines are usually lower). See 18 U.S.C. Sections 221, 3571, and 3559.

Please note that the census bureau is very serious about protecting our privacy. It releases statistical information, but not individual responses. It does not share anyone's answers with other branches of government, and it vigorously opposes subpoenas and other attempts to access people's answers. I believe no one in the entire history of American law has ever been able to make the census bureau hand over any personal information, and there is no basis for a court to issue such an order. To my knowledge nobody has ever hacked their way into the bureau's data, either.