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. County summary cards retain up to three decimals for areas below 10 square miles and one decimal for larger areas; detailed tables retain up to three decimals. If a published zero water value has a positive original AWATER field, the summary says less than 0.001 square miles and identifies the original square-meter measurement.
Population and density
Population figures are the Census Bureau’s Vintage 2025 county resident population estimates for the 50 states and the District of Columbia, and the separately published Puerto Rico municipio estimates (the April 1, 2020 base and July 1 estimates, read from the age and sex file’s total rows as documented in its file layout). Both files were retrieved October 8, 2026; their SHA-256 checksums are stored with the project, and every one of the 3,222 GEOIDs must match exactly once with the same name before the data is accepted.
Estimates are not census counts. The Census Bureau revises the whole series each year, so a later vintage can change earlier years as well as add a new one. Change since 2020 is measured from the April 1, 2020 estimates base. Density divides the latest estimate by Gazetteer land area (ALAND), so water is excluded; density rankings divide by the original square meters, with ties ordered by GEOID. A county-wide density is an average and does not describe how people are distributed within the county.
County seats, establishment years, and namesakes
These facts come from Wikidata, a community-maintained knowledge base published under CC0, retrieved October 8, 2026. Each county equivalent is matched to its Wikidata item by FIPS code (property P882). We keep only current statements: deprecated statements and those with an end date are dropped, and preferred statements are used when present. That excludes former county seats. An establishment year (P571, “inception”) is shown only when it has at least year precision and the remaining statements agree; namesakes come from P138. 3,211 of 3,222 county equivalents matched; 11 have no matching item, including Connecticut’s planning regions.
Independent cities, Alaska census areas, and some consolidated governments have no separate county seat. Some counties legitimately have two seats. Establishment can mean different legal events in different states, from colonial formation to a later reorganization, so treat the year as a guide and follow the linked Wikidata item to its references before relying on it.
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.
Cities, towns, metro areas, and ZIP codes
Community lists use the Census Bureau’s Vintage 2025 subcounty population estimates, retrieved October 22, 2026. In the 12 states where county subdivisions are general-purpose governments (the six New England states, Michigan, Minnesota, New Jersey, New York, Pennsylvania, and Wisconsin), profiles list every county subdivision: towns, townships, cities, boroughs, and the occasional unorganized area. They cover the whole county, so their populations add up to the county estimate and their land, from the 2026 county subdivision Gazetteer, is shown as a share of county land. Counties consolidated with a city, such as New York City’s boroughs and Philadelphia, list the city instead.
Elsewhere, profiles list incorporated places: cities, towns, and villages. Their populations count only the part of each place within the county, and the remainder, which the Census Bureau publishes as the balance of the county, is reported as living outside incorporated places. Census-designated places are statistical areas without their own government and are not listed. Place land area comes from the 2026 place Gazetteer and covers the whole place, including any part in another county. 8 places or subdivisions that dissolved or were renamed after the estimates’ boundary year are matched by hand or shown without an area; the list is stored with the data.
Metropolitan and micropolitan statistical areas follow the Office of Management and Budget’s July 2023 delineation: 393 metropolitan and 542 micropolitan areas in the states and Puerto Rico, leaving 1,307 county equivalents outside both. Area totals and ranks add up the member counties in this dataset.
ZIP Code Tabulation Areas come from the 2020 Census ZCTA-to-county relationship file. A ZCTA is listed when any of its land falls in the county, and “mostly inside” means more than half of its land does. Connecticut’s ZCTAs are assigned through the ZCTA-to-county-subdivision file, because towns kept their codes when planning regions replaced counties. ZCTAs approximate USPS delivery areas; they are not the Postal Service’s own boundaries, and mail-only ZIP Codes have none.
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.
Bordering counties
County profiles list the county equivalents that share a land border, derived from the same 2025 cartographic boundaries. The national locator is built as one topology, so a border between two counties is drawn from the same line in both outlines; two entries are listed as bordering when their outlines share at least one border segment. Neighbors are ordered by the length of that shared border, longest first. A few independent cities are too small to survive simplification; they are matched to the county whose outline contains their internal point.
Two limits follow from the source. Cartographic boundaries are clipped to the shoreline, so counties that face each other only across open water, such as islands, are not listed as bordering. Counties that meet at a single point, like the Four Corners, share no border segment and are not listed either. The Census Bureau’s separate county adjacency file uses full-extent boundaries and can include such water and point contacts.
Same-scale outlines
The comparison page draws both county outlines from the national locator geometry: one Albers equal-area projection for the Lower 48, with Hawaii and Puerto Rico at the same scale. Alaska is drawn at 35% in the national map, so its outlines are enlarged back to the common scale before comparison. Because the projection preserves area, drawn sizes compare fairly. Moving an outline away from its true location keeps the projection’s local rotation and slight shape distortion, and simplification removes small coastal detail, so the overlay is a visual aid; the area table is the measurement.
State size comparisons
When a profile compares a county with U.S. states, each state’s land area is the sum of the original ALAND values of its county equivalents in the same Gazetteer release. Comparisons cover the 50 states; the District of Columbia and Puerto Rico are excluded from “of the 50 states” counts. The equivalent-square figure is the square root of land area and is only a scale reference.
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.
Dataset refreshes are manual. The publisher is responsible for reviewing each release’s coverage and geographic changes before publication, recording the reviewer and review date in the repository’s review log, and running the full release checks. Automated checks validate files and calculations; they do not certify Census methodology or replace that editorial review. The current measurement and map vintages are stated above, so readers can identify the release they are using.
Reproduce or report
Download the normalized data and source checksum. To report a discrepancy, email [email protected] with the county GEOID, affected field, page URL, and original source record.