Candlelight, I'm so sorry to hear about the earthquake! I hope everyone recovers swiftly.
As much as I might want to fill out the US census, I move around so much that my information would be invalid within a few months of sending it in.
I thought the point about censuses is that they're supposed to be a snapshot of a country on a particular day. In the UK, at least, that's the case.
RoJo --
Asbo's correct. It's meant to be a snapshot of one particular day. (And it is required by law.)
The questions were simple -- name, birthdate, gender, uhh, can't remember the rest, but I think there were generally three or four other items. Since the U.S. Census is only done every ten years, and we just did one this past summer, I guess you're safe for now.

But please do fill out the questionnaire in 2020, okay?
There is a survey done every year (called the American Community Survey) that is easily confused with the Census, but it's not required to participate in it if you're chosen. (It
is a good idea to do so, though, because it helps decide where federal funding goes, community-wise).