# County population history

Imported November 6, 2026 from the U.S. Census Bureau. `scripts/import-population.py` rebuilds 65,936 dated records for all 3,142 map counties from preserved, hashed snapshots. All population values describe total residents, including people who cannot vote. No turnout percentage uses population as a voter-eligibility denominator.

The same file also contains 1,071 dated state estimates for the 50 states and D.C., 2005–2025. State estimates use the source's direct SUMLEV 40 rows for 2005–2009 and 2020–2025. For 2010–2019, each state is the sum of all its source intercensal county rows, before map filtering or geographic holds; those rows reconcile to the national source total. A state's estimate is never assembled by mixing reference years from the map county series.

County and state cards can display **reported ballots ÷ total resident population** with the population reference date. This share includes children and other ineligible residents in its denominator; it is distinct from eligible-voter or registered-voter turnout. A 2026 share uses a dated 2025 estimate and provisional reported ballots.

| Years displayed | Source | Join and checks |
|---|---|---|
| 2005–2009 | [2000–2010 intercensal county totals](https://www2.census.gov/programs-surveys/popest/datasets/2000-2010/intercensal/county/co-est00int-tot.csv) | County FIPS; each annual county sum equals the source state total. Shannon/Oglala Lakota and Wade Hampton/Kusilvak use documented name/code changes. |
| 2010–2019 | [2010–2020 intercensal county totals](https://www2.census.gov/programs-surveys/popest/tables/2010-2020/intercensal/county/co-est2020int-pop.xlsx) | Exact county name and state join to Census FIPS registry; all 3,143 source rows reconcile to each annual national total. This is the Census-preferred intercensal series for the decade. |
| 2020–2025 | [Vintage 2025 county estimates](https://www2.census.gov/programs-surveys/popest/datasets/2020-2025/counties/totals/co-est2025-alldata.csv) | Exact county FIPS; all six annual county sums reconcile to source state totals. |

The card selects the latest July 1 reference year at or before the selected election year. Map-only mode selects the latest available estimate. Estimates can be revised in a later vintage. The latest released county series is July 1, 2025; a 2026 estimate is not invented. The displayed population percentage describes reported ballots in the selected cycle divided by the dated resident estimate. It does not compare population growth with a previous year.

Geographic exceptions:

- The map uses 2017 county outlines. Connecticut's historical eight counties retain [Vintage 2021 estimates](https://www2.census.gov/programs-surveys/popest/datasets/2020-2021/counties/totals/co-est2021-alldata.csv); newer planning regions are not allocated to these old counties. The older reference year and a note appear on the card.
- Valdez-Cordova retains [Vintage 2019 estimates](https://www2.census.gov/programs-surveys/popest/datasets/2010-2019/counties/totals/co-est2019-alldata.csv). Later successor census areas are not allocated onto the old map polygon.
- Bedford County's pre-2013 population is withheld because the former independent city later merged into that county. Neither the city's population nor its elections are silently reassigned.
- Other same-FIPS observations retain the Census source's vintage geography. Historic estimates and modern outlines do not establish an exact historical boundary reconstruction.

Raw files and receipts: `scripts/source-data/population/`. Public data, manifest, and source controls: `public/data/population/`. Unused Census vintages are retained as research evidence; they do not override the series listed above.