The district has four unincorporated areas: Rose Hills (North Whittier), East Whittier, South Whittier and Los Nietos is assisted by the Pico Rivera Sheriff’s and the Los Angeles County Fire Department. West Whittier-Los Nietos is a census-designated place in , near the San Gabriel River and the San Gabriel River (I-605) Freeway. The population was 25,540 at the 2010 census, up from 25,129 at the 2000 census. The census area consists of separate unincorporated communities of Los Nietos, Spanish for "the grandchildren.”
Los Nietos is among the oldest communities in Southern California. The Los Nietos School District was established in 1861 and a Methodist circuit centered on the city was founded in 1867. The community grew up around the Rancho Los Nietos and its constituent rancho Rancho Santa Gertrudes.