County Maps US

Los Alamos County, New Mexico

A county in New Mexico, ranked 20 of 33 by population.

CountyFIPS 35028

Within New Mexico
Los Alamos County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Los Alamos, the county seat, located via the 2025 Census Gazetteer.

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Population
19,407
-7 (0%) since 2020
Land area
109.1
square miles. A further 0.1% of the total area is water
Population density
178
people per square mile, computed rather than published
County seat
Los Alamos
Seat of county government.
Established
1949
76 years ago
Largest city
Not available
No incorporated place lies within this county.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of Los Alamos County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of Los Alamos County, New Mexico from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 737 by 800 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where Los Alamos County ranks

Position among the 33 counties of New Mexico, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn New MexicoNationally
Population19,40720th of 331,864th of 3,144
Land area109.1 sq mi33rd of 333,081st of 3,144
Population density178 per sq mi2nd of 33608th of 3,144
Median household income$147,1391st of 328th of 3,143

Full data for Los Alamos County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population19,407Vintage 2025 Population Estimates
Population in 202019,414Vintage 2025 Population Estimates
2020 estimates base?19,416Vintage 2025 Population Estimates
Land area109.1 sq mi2025 Gazetteer Files
Water area0.08 sq mi2025 Gazetteer Files
Total area109.2 sq mi2025 Gazetteer Files
Population density?178 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$147,139American Community Survey 2020-2024 5-Year Estimates
Median home value$495,800American Community Survey 2020-2024 5-Year Estimates
Median age39.3American Community Survey 2020-2024 5-Year Estimates
Households8,247American Community Survey 2020-2024 5-Year Estimates
Housing units8,713American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
+29
189 births, 160 deaths
Net migration
-53
More people moved out than moved in.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 3 areas bordering Los Alamos County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
Sandoval CountyNew Mexico39 mi159,565
Santa Fe CountyNew Mexico18 mi156,907
Rio Arriba CountyNew Mexico2.6 mi39,832

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

All 33 counties of New Mexico

Open the interactive New Mexico county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.