The one-year American Community Survey (ACS) data are the most current. One-year ACS data sets provide information for areas with populations of 65,000 persons or more. These data are only available for Fairfax County as a whole.
The American Community Survey (ACS) was developed to replace the decennial census "long-form" information. The subject areas covered by the ACS are similar to those on the decennial census “long-form” survey but the ACS information is interpreted differently. The primary purpose of the ACS is to describe characteristics over a period of time, not to provide point-in-time counts.
The ACS provides three data sets - one-year, three-year and five-year estimates. Data between the one-, three- and five-year data sets should not be mixed together. The estimates from these different data sets are not comparable because they reflect different time periods. Data in the one-year data set are more current but the multi-year data sets provide information for smaller levels of geography. Generally, users should use the most current ACS data set that supports the smallest level of geography being analyzed.
Data users need to be careful about drawing conclusions about differences between ACS estimates. Users of ACS data must check the margin of errors (MOE) associated with estimates to determine if they are statistically different.
Three-year ACS data sets provide information for areas with populations of 20,000 persons or more. Three-year ACS data are available for some Fairfax County sub-geographies. The three-year ACS data can be obtained directly from the U.S. Census Bureau's American FactFinder tool.