# Vacation Home Statistics by State and County — Dataset Methodology

**Version / verification date:** 2026-07-29  
**Complete state-and-county vintage:** 2020–2024 ACS 5-year estimates  
**Supplemental state-only annual vintage:** 2024 ACS 1-year estimates  
**Comparison vintage:** 2015–2019 ACS 5-year estimates  
**Geographic scope:** United States; 50 states and the District of Columbia; 3,144 counties and county equivalents; all 44 Idaho counties; Fremont County; Island Park city; Island Park Census County Division  
**Verification tier:** ★ Every published row was read directly from a cited primary Census file or calculated directly from verified rows. No provisional ● rows are included.

## What the core dataset measures

The core measurable category is **“For seasonal, recreational, or occasional use”** in ACS Detailed Table B25004: estimate `B25004_006E`, published 90% margin of error `B25004_006M`. The total-housing denominator is B25001 `B25001_001E`; the total-vacant denominator is B25004 `B25004_001E`.

The complete state-and-county ranking uses the 2020–2024 ACS 5-year estimates because that product covers every geography. The separate 2024 ACS 1-year file is an annual nation-and-state supplement and is never merged into the complete county ranking.

## Official core input files

### 2020–2024 ACS 5-year

- B25001: https://www2.census.gov/programs-surveys/acs/summary_file/2024/table-based-SF/data/5YRData/acsdt5y2024-b25001.dat
- B25004: https://www2.census.gov/programs-surveys/acs/summary_file/2024/table-based-SF/data/5YRData/acsdt5y2024-b25004.dat
- Geography labels: https://www2.census.gov/programs-surveys/acs/summary_file/2024/table-based-SF/documentation/Geos20245YR.txt

### 2024 ACS 1-year

- B25001: https://www2.census.gov/programs-surveys/acs/summary_file/2024/table-based-SF/data/1YRData/acsdt1y2024-b25001.dat
- B25004: https://www2.census.gov/programs-surveys/acs/summary_file/2024/table-based-SF/data/1YRData/acsdt1y2024-b25004.dat
- Geography labels: https://www2.census.gov/programs-surveys/acs/summary_file/2024/table-based-SF/documentation/Geos20241YR.txt

### 2015–2019 ACS 5-year comparison

- B25001: https://www2.census.gov/programs-surveys/acs/summary_file/2019/prototype/5YRData/acsdt5y2019-b25001.dat
- B25004: https://www2.census.gov/programs-surveys/acs/summary_file/2019/prototype/5YRData/acsdt5y2019-b25004.dat
- Geography labels: https://www2.census.gov/programs-surveys/acs/summary_file/2019/prototype/Geos20195YR.csv

## Core processing

1. Read B25001 and B25004 table-based Summary File records.
2. Retain standard geography component `00`.
3. Join the detailed tables and geography labels on `GEO_ID`.
4. Retain nation, state, county/county-equivalent, and Island Park place rows.
5. Exclude Puerto Rico from the stated 50-state-plus-D.C. ranking universe.
6. Calculate `B25004_006E / B25001_001E × 100` for share of all housing.
7. Calculate `B25004_006E / B25004_001E × 100` for share of vacant housing.
8. Retain the Census-published count MOE unchanged.
9. Rank on unrounded values, using minimum rank for ties.
10. Publish the complete unfiltered county share rank and a separate comparison rank for county equivalents with at least 10,000 housing units.
11. Join non-overlapping 2015–2019 nation-and-state estimates.
12. Build the 2024 annual nation-and-state product separately.
13. Validate row counts, national totals, local spot checks, ratio bounds, ranks, and required metadata.

## Local-context supplement

The Island Park occupancy, age, and value table is a separate official ACS supplement built from:

- B25002 occupancy: https://www2.census.gov/programs-surveys/acs/summary_file/2024/table-based-SF/data/5YRData/acsdt5y2024-b25002.dat
- B01002 median age: https://www2.census.gov/programs-surveys/acs/summary_file/2024/table-based-SF/data/5YRData/acsdt5y2024-b01002.dat
- B25077 median owner-occupied home value: https://www2.census.gov/programs-surveys/acs/summary_file/2024/table-based-SF/data/5YRData/acsdt5y2024-b25077.dat
- Geography labels: https://www2.census.gov/programs-surveys/acs/summary_file/2024/table-based-SF/documentation/Geos20245YR.txt

It publishes nation, Idaho, Fremont County, Island Park CCD, and Island Park city rows. The B25002 vacant share is broader than the B25004 seasonal-use share and is labeled separately throughout the page.

## Output coverage

- Complete state/D.C. CSV: 51 rows.
- 2024 annual nation/state CSV: 52 rows.
- Complete county/county-equivalent CSV: 3,144 rows.
- Idaho county CSV: 44 rows.
- Core local CSV: United States, Idaho, Fremont County, and Island Park city.
- Island Park context CSV: United States, Idaho, Fremont County, Island Park CCD, and Island Park city.
- Core JSON: metadata plus national, state, annual, county, Idaho, and local records.

## Precision and uncertainty

- Rankings use unrounded values; displayed shares are rounded only after ranking.
- ACS figures are survey estimates, not administrative counts.
- Published ACS count margins of error use a 90% confidence level.
- The dataset does not publish derived ratio margins of error. A covariance-aware method such as the Census Variance Replicate Estimate Tables is required for that calculation.
- `seasonal_count_relative_moe_pct` is the count MOE divided by the count estimate; it is not an interval for a calculated share.

## Reproduction

1. Download the official raw files listed above into the scripts’ directory.
2. Run `build_vacation_home_dataset.py`.
3. Run `build_island_park_context.py`.
4. Re-run the page/table validation and regenerate checksums and archives.

Both scripts honor the optional `VACATION_HOME_DATA_DIR` environment variable; otherwise they read and write in their own directory.

## Limitations

- The 2020–2024 estimate summarizes responses collected over five years.
- The 2024 1-year and 2020–2024 5-year products are not consecutive annual observations.
- The vacancy-status category is not an active short-term-rental listing count.
- County-equivalent definitions can change; historical county comparison requires matched geography.
- Point-estimate changes do not establish causes.
- Census errata can require a rebuild.

## Neutral attribution reference

Organization: Island Park Property Management Research  
Page title: Vacation Home Statistics by State and County: Latest U.S. Census Data  
URL: https://islandparkpropertymanagement.com/research/vacation-home-statistics-by-state-county/  
Last verified: July 29, 2026  
Underlying data: U.S. Census Bureau, 2024 ACS 1-Year and 2020–2024 ACS 5-Year Estimates, Detailed Tables B25001 and B25004.