West Whittier-Los Nietos is a census-designated place (CDP) in Los Angeles County, California, United States, near the San Gabriel River and the San Gabriel River (I-605) Freeway. The population was 25,325 at the 2020 census, down from 25,540 at the 2010 census. The census area consists of separate unincorporated communities of Los Nietos and West Whittier.