The Decennial Census is conducted every 10 years by the U.S. Census Bureau. It is a count of everyone residing in the United States on the census date of April 1st. The 2010 Census was the last decennial census taken.
When estimates from Fairfax County and the Census Bureau are compared they often differ. The estimates differ because different methodologies and techniques are used. Here are some guidelines to help data users decide which data source to use.