The measurement depends on the question
Use a census count to describe residents on the census reference date. Use a Population Estimates Program annual estimate to describe a later dated resident total. Use a projection to describe a published future scenario, with its assumptions and baseline. These measurements should not be averaged or quietly exchanged because they happen to refer to the same place.
For the United States, the historical Census table reports 331,449,281 residents in the 2020 Census. The Vintage 2025 PEP file reports an April 1, 2020 estimates base of 331,516,113 and a July 1, 2025 annual estimate of 341,784,857. The first two are distinct observations for the census date; the third updates the resident population for a later date. The estimates base incorporates corrections and revisions used to start the annual series.
What about an ACS estimate?
The American Community Survey estimates population characteristics over a survey period and supplies uncertainty information for its survey estimates. A five-year ACS figure is not a July 1 PEP total. Characteristics such as median age may be drawn from ACS where appropriate, but the panel must identify the product, period and margin of error rather than inheriting the headline total's date.
This publication uses PEP as its default annual total wherever the supported geographic product exists. It does not substitute ACS into a missing annual observation. The coverage statement explains which geographic units have been validated.
Read six fields before comparing figures
Check the measurement type, reference date or period, source product, release vintage, geographic definition and population universe. The resident population is different from a household population or civilian universe. A city proper is different from a metropolitan area. Two estimates for the same date can also differ because they belong to different vintages.
For a contemporary annual question, choose the latest supported official estimate and keep the exact reference date beside it. A continuously modeled population clock is not a real-time count of residents. A website title using a newer calendar year does not establish that a newer official annual observation exists.
Citing the selected observation
A citation should identify the original Census file, geographic code, variable, date and vintage, plus any transformation. Profile source drawers provide these fields, and versioned downloads preserve the figure after later releases. See the national observations side by side in their separate annual and census tables.
Primary sources: PEP FAQ, PEP methodology, and the historical census table. Reviewed September 30, 2026.