The American Community Survey (ACS) makes use of the Population Estimates Program’s (PEP) official population estimates as survey controls in order to improve the ACS estimates for those characteristics which overlap with the PEP. This results in ACS estimates being equal or similar to the PEP estimates for total population as well as having similar age, sex, Hispanic, and non-Hispanic by race distributions. In addition, the ACS estimates for the total group quarters population are equal to the PEP estimates at the state and national level.

As part of an ongoing series of user notes that explain the effects of the population controls on the ACS since 2020, this user note focuses on changes to the methodology used for the Vintage 2025 PEP estimates which the 2025 ACS products use as its source for control totals.

For the first time since 2021, the population controls are no longer created from the blended base. The starting point for the Vintage 2025 estimates is the 2020 Census via the Modified Age and Race Census (MARC) file. The base population uses the full demographic characteristic detail from the MARC file as well as corrections for age distribution and boundary updates as of January 1, 2025. For Puerto Rico, the base population is developed from the MARC file using age and sex detail.

Additionally, there have been updates to the migration methodology incorporated into the Vintage 2024 estimates. The geographic distributions of migration at the state and county level have been improved and updates to both immigration and emigration have been incorporated as well. For more information on how the Vintage 2025 estimates were updated please refer to the Vintage 2025 Release Notes.​