Data Methodology

The Census Bureau’s Population Estimates Program data by county includes details like counts by age, race, or ethnicity and goes back for decades. But how the Census Bureau reported and grouped those populations changed over time.

To provide the most detail across all available data, USAFacts combined the census data on race and ethnicity into three groupings.

Any comparison of data from before 1990 only includes the “white,” “Black,” and “Other” race/ethnicity categories. These were the only categories included before 1990 for the available data.

Any comparison with the 1990 census to newer data will include the “white,” “Black,” and two categories added that year: “American Indian/Alaska Native” and “Asian or Pacific Islander.”

Data from 2000 onward will also include the “Two or more race” category. This category can’t be compared prior to 2000. Comparison pages include footnotes explaining that pre-2000 and post-2000 data comparisons will result in lower values for the separate race categories in proportion to the expected “two or more race” population.

For population by age, USAFacts grouped people ages 0–4 in different ways depending on the census. The “less than 1” and “1 to 4” groups for the 1990 and 2000 censuses were combined to create a consistent “0 to 4” group across all available data.

The Census Bureau releases annual provisional population estimates based on the previous decennial census and other data on births, deaths, and migration/immigration. Every decade, the Bureau reconciles these estimates and releases final data.

These provisional estimates are “postcensal estimates,” and the final estimates are “intercensal estimates.” USAFacts used the final intercensal estimates for 1970 through 2009 and the provisional postcensal estimates for 2010 and after. The most recent county-level data available by age, race, sex, and ethnicity are the Vintage 2020 Population Estimates (census.gov) for 2010 to 2019 and the Vintage 2021 Population Estimates (census.gov) for 2020 and 2021. We will update this experience, including the 2010-2019 estimates, when the Bureau releases county-level 2010–2020 intercensal estimates by age, sex, race, and ethnicity.

Use caution when interpreting population changes that use different “postcensal” version estimates. The 2010-2020 postcensal estimates are known to underestimate the population by about 1% nationally. This underestimate is, effectively, zero for 2010 and grows each year to reach 1% by 2020. The estimate years differ from the base 2010 decennial census; underestimates will be resolved in 2023 when the Census Bureau releases its 2010-2020 intercensal estimates.