Add me to the growing list of those who didn't fill it out.
When they came to my house to ask about it, I looked them in the eye, and said, "Two." When she asked what I meant by that, I said, "The Constitution requires me to tell you 'two' and nothing more. That's how many people live here."
They never sent anyone after me, but that's what I would have told them, too!
I had a great conversation with a census worker in 1990.
She came to my house and couldn't understand why I wouldn't want to tell the government about myself. She assured me that all the information would remain private. That's when I informed her that while I loved Reagan as President, he had census data given to various law enforcement agencies.
She responded with promises of the great things the government would do with the information. I offered the truism that excepting law enforcement and defense, government was incapable of doing anything well. She said, "Well, the government of Person County just did a great thing. They just established higher standards for rental housing."
"That's horrible!" I replied. " I know some of the people who own that rental housing. They'll burn it down before they put another dime into it. People will be thrown out into the streets from houses they've been in all their lives. Or landlords will have to raise rents above what those folks can afford. How can you be so heartless?" She had no response to that.