According to the US Census papers the response and participation in the US Census is required by law.
However I have never once participated in the US Census and never have I been fined or been taken to court or anything.
What happens when you don't take the US Census is the Census will send out a Census Taker to your house to harass you at your house.
All you need to do is tell them to leave and shut the door on them or do not answer the door.
What I do is just go on vacation when they usually come around so I never have to see them.
The fine for not taking the Census is around $100.00 so it's not that bad but I have never taken the Census survey because it's my right at as a Free person in the USA.