The following data attributes are produced quarterly or monthly by the Prince William County Department of Information Technology's Geospatial Technology Services and other sources. If you are looking for the county's official demographic dataset, please see the Standard Data Dictionary.

*Notes about the population estimates:

• The county's Group Quarters estimate is 4,935 people. This is included in the population estimate.
• 2010 Census tabulation block data are adjusted to the latest American Community Survey Estimates of the county to recalculate occupancy rates and average household size for quarter 4 of each year. Census PUMS (Public Use Microdata Sample) data are used from PUMAS 51244, 51245, and 51246 from the American Community Survey to also calculate weighted average occupancy rates and household size by housing unit type. These estimates are combined with the adjusted 2010 tabulation block estimates to produce occupancy and average household size by unit type. Changes to these values directly impact household and population totals.
• Age-restricted (ages 55+) housing is taken into account. Average household size is different in these communities. In 2020 Q4 there are an estimated 5,749 age-restricted housing units in the county. U.S. Census data from the 2012-2016 American Community Survey 5-Year Estimates informs us that there was a population of 82,640 residents ages 55+ and households with the main householder ages 55+ at 43,821. This translates to about 1.89 persons per household. An occupancy rate of 100% was used for age-restricted units. In all, it is estimated that 10,866 residents live in age-restricted units.
• Source data contain margins of error. Average household size and occupancy data from the American Community Survey represent a sample of the population. Data made available to the public are estimates and contain (+/- x) where x = the margin of error for each respective demographic variable. Data from the ACS are used in generating quarterly estimates. The following are the overall margins of error for the data used to generate the county's household size and occupancy rates:

NOTES:

• The quarterly estimates and annual estimates from 2010 to 2016 were restated in February of 2017 to reflect the markedly higher estimates generated starting at 2016 Quarter 3 by smoothing over prior estimates. For more information about these changes and corresponding methods, see the following PDF: Redistributing Quarterly Population Estimates, 2010-2016
  

• Compare PWC's estimates to the most current estimates and projections of PWC's population:
• U.S. Census ACS 1-Year Estimate (July 2019): 470,335
  
• Weldon Cooper Center (July 1, 2020): 468,497
  
• COG 2020 Projection (Round 9.1): 467,900
  

QUARTERLY ESTIMATE HISTORY *

• The quarterly estimates for 2017 were restated in April 2018, and in February 2017 the quarterly estimates were restated back to 2010.
  
• The quarterly estimates for 2018 and 2019 were restated in March 2020. This followed new occupany and average household size data in conjunction with lowered average household sizes assigned to units in age-restricted communities applied to 2019 Q4 estimates.