Rancho Los Alamitos takes its name from an 1834 Mexican partition of the 1784 Rancho Los Nietos, a Spanish concession, covering an area in present-day California's southwestern Los Angeles County and northwestern Orange County. Los Alamitos means the Little Cottonwoods or Poplars in Spanish, after the native Fremont Cottonwood trees there.

Rancho Los Nietos was one of the first, and the largest, Spanish land concession in Alta California. Located in present-day Los Angeles County and Orange County, California. Rancho Los Nietos was awarded to Manuel Nieto in 1784. After an appeal by the San Gabriel Mission padres, Rancho Los Nietos was later reduced and Rancho Paso de Bartolo was once again a possession of the mission. The rest of the rancho remained intact until 1834, when Governor Jose Figueroa officially declared the Rancho Los Nietos grant under Mexican rule and ordered its partition into six smaller ranchos.