West Whittier-Los Nietos is located at 33°58′34″N 118°4′8″W (33.976113, -118.069000), or about three miles (5 km) northwest of Whittier.
According to the United States Census Bureau, the CDP has a total area of 2.5 square miles (6.5 km2), all land.
The 2010 United States Census reported that West Whittier-Los Nietos had a population of 25,540. The population density was 10,138.5 people per square mile (3,914.5/km²). The racial makeup of West Whittier-Los Nietos was 15,170 (59.4%) White (9.3% Non-Hispanic White), 254 (1.0%) African American, 372 (1.5%) Native American, 393 (1.5%) Asian, 43 (0.2%) Pacific Islander, 8,404 (32.9%) from other races, and 904 (3.5%) from two or more races. Hispanic or Latino of any race were 22,369 persons (87.6%).
The Census reported that 25,446 people (99.6% of the population) lived in households, 44 (0.2%) lived in non-institutionalized group quarters, and 50 (0.2%) were institutionalized.
There were 6,698 households, out of which 3,282 (49.0%) had children under the age of 18 living in them, 3,684 (55.0%) were opposite-sex married couples living together, 1,319 (19.7%) had a female householder with no husband present, 598 (8.9%) had a male householder with no wife present. There were 427 (6.4%) unmarried opposite-sex partnerships, and 49 (0.7%) same-sex married couples or partnerships. 843 households (12.6%) were made up of individuals and 466 (7.0%) had someone living alone who was 65 years of age or older. The average household size was 3.80. There were 5,601 families (83.6% of all households); the average family size was 4.07.
The population was spread out with 6,901 people (27.0%) under the age of 18, 2,742 people (10.7%) aged 18 to 24, 7,220 people (28.3%) aged 25 to 44, 5,825 people (22.8%) aged 45 to 64, and 2,852 people (11.2%) who were 65 years of age or older. The median age was 33.7 years. For every 100 females there were 97.0 males. For every 100 females age 18 and over, there were 93.5 males.
There were 6,923 housing units at an average density of 2,748.2 per square mile (1,061.1/km²), of which 4,897 (73.1%) were owner-occupied, and 1,801 (26.9%) were occupied by renters. The homeowner vacancy rate was 1.0%; the rental vacancy rate was 5.5%. 18,510 people (72.5% of the population) lived in owner-occupied housing units and 6,936 people (27.2%) lived in rental housing units.
According to the 2010 United States Census, West Whittier-Los Nietos had a median household income of $60,525, with 9.4% of the population living below the federal poverty line.
As of the census of 2000, there were 25,129 people, 6,720 households, and 5,597 families residing in the CDP. The population density was 9,997.3 inhabitants per square mile (3,865.5/km²). There were 6,857 housing units at an average density of 2,728.0 per square mile (1,054.8/km²). The racial makeup of the CDP was 53.06% White, 0.57% African American, 1.25% Native American, 1.63% Asian, 0.20% Pacific Islander, 38.49% from other races, and 4.79% from two or more races. Hispanic or Latino of any race were 83.07% of the population.
There were 6,720 households out of which 43.5% had children under the age of 18 living with them, 59.7% were married couples living together, 16.3% had a female householder with no husband present, and 16.7% were non-families. 13.5% of all households were made up of individuals and 6.9% had someone living alone who was 65 years of age or older. The average household size was 3.73 and the average family size was 4.04.
In the CDP, the population was spread out with 30.9% under the age of 18, 10.8% from 18 to 24, 29.7% from 25 to 44, 18.2% from 45 to 64, and 10.4% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 96.2 males. For every 100 females age 18 and over, there were 91.7 males.
The median income for a household in the CDP was $45,921, and the median income for a family was $47,699. Males had a median income of $33,012 versus $26,057 for females. The per capita income for the CDP was $14,417. About 6.3% of families and 8.9% of the population were below the poverty line, including 9.2% of those under age 18 and 6.8% of those age 65 or over.
The area is served by the Whittier Union High School District, primarily Pioneer High. For elementary school, the area is served by the Los Nietos School District and the Whittier City School District. Two middle schools are in the area (Katherine Edwards and Los Nietos) as are several elementary schools (Aeolian, Nelson, Phelan, Sorensen and West Whittier)
In the state legislature West Whittier-Los Nietos is located in the 30th Senate District, represented by Democrat Ronald S. Calderon, and in the 57th Assembly District, represented by Democrat Ian Calderon. Federally, West Whittier-Los Nietos is located in California's 38th congressional district, which is represented by Democrat Linda Sánchez.
The Los Angeles County Sheriff's Department (LASD) operates the Pico Rivera Station in Pico Rivera, serving West Whittier.