Adjacent counties

• Rio Arriba County – north, northwest, northeast
• Santa Fe County – east
• Sandoval County – south, southwest, northwest

Pueblos with adjacent territories

• Santa Clara Pueblo – northeast
• San Ildefonso Pueblo – east

National protected areas

• Bandelier National Monument (part)
• Santa Fe National Forest (part)

2000 census

As of the 2000 census,^[10] there were 18,343 people, 7,497 households, and 5,337 families living in the county. The population density was 168 people per square mile (65 people/km²). There were 7,937 housing units at an average density of 73 units per square mile (28/km²). The racial makeup of the county was 90.3% White, 0.4% Black or African American, 0.6% Native American, 3.8% Asian, <0.1% Pacific Islander, 2.7% from other races, and 2.3% from two or more races. 11.8% of the population were Hispanic or Latino of any race.

There were 7,497 households, out of which 33.5% had children under the age of 18 living with them, 62.7% were married couples living together, 5.7% had a female householder with no husband present, and 28.8% were non-families. 24.9% of all households were made up of individuals, and 6.7% had someone living alone who was 65 years of age or older. The average household size was 2.43 and the average family size was 2.92.

In the county, the population was spread out, with 25.8% under the age of 18, 4.4% from 18 to 24, 27.7% from 25 to 44, 30.0% from 45 to 64, and 12.1% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 101.40 males. For every 100 females age 18 and over, there were 99.70 males.

The median income for a household in the county was $78,993, and the median income for a family was $90,032. Males had a median income of $70,063 versus $40,246 for females. The per capita income for the county was $34,646. 2.9% of the population and 1.9% of families were below the poverty line. 1.8% of those under the age of 18 and 4.7% of those 65 and older were living below the poverty line.

2010 census

As of the 2010 census, there were 17,950 people, 7,663 households, and 5,199 families living in the county.^[11] The population density was 164.4 inhabitants per square mile (63.5/km²). There were 8,354 housing units at an average density of 76.5 units per square mile (29.5 units/km²).^[12] The racial makeup of the county was 87.8% white, 6.0% Asian, 0.8% American Indian, 0.6% black or African American, 0.1% Pacific islander, 2.2% from other races, and 2.6% from two or more races. Those of Hispanic or Latino origin made up 14.7% of the population.^[11] In terms of ancestry, 18.9% were German, 16.5% were English, 13.2% were Irish, and 6.5% were American.^[13]

Of the 7,663 households, 31.3% had children under the age of 18 living with them, 58.1% were married couples living together, 6.4% had a female householder with no husband present, 32.2% were non-families, and 28.5% of all households were made up of individuals. The average household size was 2.33 and the average family size was 2.86. The median age was 44.3 years.^[11]

The median income for a household in the county was $103,643 and the median income for a family was $118,993. Males had a median income of $93,040 versus $51,753 for females. The per capita income for the county was $49,474. About 1.4% of families and 2.4% of the population were below the poverty line, including 1.8% of those under age 18 and 2.4% of those age 65 or over.^[14]

County council

The county council was created by the Los Alamos County Charter. The council consists of seven members elected at large for four-year, staggered terms. Each year the seven councilors select the new chair and vice chair. ^[15]

County offices

Current energy resources

Starting in 1985, Los Alamos County, including both the White Rock and Los Alamos communities, has shared energy resources with the Los Alamos National Laboratory.^[19]

Future energy resources

Both Los Alamos County and the Los Alamos National Laboratory are trying to reduce their respective carbon emissions^[19] in order to help mitigate the continually worsening dangers of climate change.^[21] In 2015, Los Alamos County joined with the Utah Associated Municipal Power Systems in the Carbon Free Power Project.^[22] The Project planned to use NuScale Power’s Small Module Reactor design to provide nuclear energy to counties across the United States, but was cancelled in 2023 because of cost increases.^[23] Los Alamos’ history is tied to nuclear energy, which has an environmental impact comparable to that of renewables as a source of domestic power.^[24] This is true of both large and small module reactors.^[25]