The deadline for mailing back your 2010 census was April 16, 2010. However, on May 1st, census takers will begin going door-to-door to roughly 1/3 of households that did not mail back their forms. They also will verify that housing units indicated as "unoccupied" to the U.S. Census by the postal service or others are indeed unoccupied and vacant.
All personal information is confidential and is protected by federal law.
For additional information please see the 2010 Census website at http://2010.census.gov/2010census/