The U.S. Census Bureau calculates population figures each year through its Population Estimates Program. These population estimates cover the nation, states, counties, cities, and towns, according to the agency. The program also tracks housing unit estimates for the nation, states, and counties, as well as population figures for the Commonwealth of Puerto Rico and its municipios.
Calculating annual change
To estimate the population, the Census Bureau utilizes current data on births, deaths, and migration. The agency measures demographic components of change starting from the most recent decennial census up to the current estimate year, which is known as the vintage year. The estimates detail national, state, and county resident populations by age, sex, race, and Hispanic origin, according to the Census Bureau. At the national level, estimates also cover households, civilians, the civilian noninstitutionalized population, and residents plus Armed Forces overseas.
Producing area estimates
The Census Bureau publishes population totals for cities, towns, and other subcounty areas. The agency also produces estimates for metropolitan and micropolitan statistical areas. According to the Census Bureau, these metropolitan and micropolitan areas consist of one or more whole counties or equivalent entities. The agency aggregates the appropriate county-level population estimates to produce these specific area figures.
Revising past estimates
Every time the Census Bureau releases new annual estimates, it revises the entire time series of data going back to the last census. The latest vintage of data supersedes all previously produced estimates for those dates, according to the agency. The older, superseded estimates are then archived on an agency site called FTP2. The agency publishes methodology statements alongside the data to provide an overview of the input data, methods, and processes used to produce the estimates.
Protecting confidential data
Before publishing the numbers, the Census Bureau reviews the population and housing unit estimates products to ensure appropriate access and use. This review provides disclosure avoidance protection for the confidential source data used to create the estimates, according to the agency. The review process is approved by a Disclosure Review Board, and the data is tracked with a Data Management System number.
How the estimates are used
The federal government relies on the annual population estimates to allocate funding across the country, according to the Census Bureau. The figures also serve as survey controls and as denominators for vital rates and per capita time series. Additionally, the agency says the data functions as an indicator of recent demographic changes.