Measurement source
US County Area uses the U.S. Census Bureau’s 2026 national Counties Gazetteer ZIP, retrieved September 27, 2026. The normalized dataset contains 3,222 county and county-equivalent records. Census Gazetteer documentation describes the release and coverage.
Fields and units
We retain USPS state code, five-digit GEOID, official NAME, original integer ALAND and AWATER in square meters, published ALAND_SQMI and AWATER_SQMI, and INTPTLAT/INTPTLONG. Source names retain accents; existing page slugs remain stable.
- Total square miles: ALAND_SQMI + AWATER_SQMI, rounded to the source precision of three decimal places.
- Water share: AWATER_SQMI ÷ total square miles × 100.
- Square kilometers: published square miles × 2.58998811.
- Acres: published square miles × 640.
Conversions from the published square-mile fields can differ slightly from direct conversions of square-meter values because the published fields are already rounded. Summary cards show one decimal at most; detailed tables retain up to three decimals.
Ranking rules
Land rankings sort the original integer ALAND field. Total-area rankings sort ALAND + AWATER. Water-share rankings sort the calculated percentage above. Exact ties use ascending GEOID for a deterministic order. Each record receives a sequential position rather than a shared competition rank.
State land ranks use only that state’s records. National ranks include Puerto Rico and the District of Columbia. The “outside Alaska” ranking excludes Alaska only; it retains Hawaii and Puerto Rico. Pagination changes the visible rows, not the rank calculation.
Context and comparisons
A state’s county-equivalent median is the middle land-area value after sorting; for an even number of records, it is the average of the middle two values. A county’s share of state land divides its land square miles by the sum of all county land square miles in that state. This sum can differ from a separately published state measurement.
Similar-sized counties minimize the absolute difference in original land square meters within the same state. They are not necessarily neighbors. Comparison bars use land square miles and share a common scale within each comparison. Percentage difference uses the smaller county’s land area as the denominator; it is omitted when that denominator is zero.
The national median uses all county equivalents, including DC and Puerto Rico, with one observation per record. The median water share is the middle of the individual county percentages, not the national water total divided by total area. State summaries instead calculate combined water share as summed water divided by summed land plus water. These two measures give different weight to counties of different sizes.
The count of smaller counties uses a strict comparison of original ALAND values and excludes exact ties. Adjacent national rank positions are the preceding and following records in the full land ranking, not geographic neighbors. The change from land rank to total-area rank compares two separate orders; a county can move down when other counties gain more area from water. Ranking-page summaries describe only the entries on that page, including their state-level representation.
Coverage and county equivalents
The dataset covers 50 states, the District of Columbia, and Puerto Rico. It includes Louisiana parishes, Alaska boroughs and census areas, Connecticut planning regions, independent cities, and Puerto Rico municipios. Other U.S. island areas are outside this Gazetteer’s coverage. See our county-equivalent guide.
Map source and limitations
County outlines come from the 2025 Census cartographic county boundaries, 1:500,000, retrieved 2026-09-27. We match them by GEOID and render each locally with an azimuthal equal-area projection centered on its representative point. Each image is fitted independently and is not a visual size comparison with other county images.
These generalized outlines simplify coastlines and other details. They are illustrations, are from a different release than the area data, and are never used to compute our measurements. The Census boundary-file description explains simplification and offshore clipping.
The national locator map on the home page and county profiles uses the same boundaries in a composite equal-area layout. The Lower 48, Hawaii, and Puerto Rico share one scale; Alaska is reduced to 35% of that scale so it fits as an inset. Borders are simplified for display, and the western Aleutians beyond 180° and the Northwestern Hawaiian Islands are omitted. Counties too small to see at that size are marked with a ring at the Census internal point.
Coordinates and legal limits
Census internal points represent locations inside the geography. They are not necessarily centroids or government office addresses. Neither the maps nor these statistical measurements establish legal property lines or resolve jurisdiction disputes.
Quality checks and updates
Data refreshes validate identifiers, unique routes, nonnegative finite measurements, and coordinate ranges before replacing the dataset. Release checks cover ranking order, source metadata, all county map files, internal links and assets, generated metadata, and the sitemap. Browser tests cover search, comparison, rankings, and responsive layouts. A new data vintage requires a deliberate source review and rebuild; retrieval dates are recorded in source metadata.
Reproduce or report
Download the normalized data and source checksum. To report a discrepancy, email corrections@uscountyarea.com with the county GEOID, affected field, page URL, and original source record.