The United States has had a census every ten years since 1790 (the decennial Census of Population and Housing).
As the decennial census data are outdated by the time they are published, an ongoing American Community Survey (ACS) provides more accurate demographic profiles on an annual basis.
The Comparison of Census 2000 and ACS 2005 document provides general comparability issues between the 2000 Census and the 2005 American Community Survey.
There are other U.S. censuses besides the Census of Population and Housing: