Lemon Grove is a city in San Diego County, California, United States. The population was 27,627 at the 2020 census, up from 25,320 at the 2010 census.
The area that eventually became Lemon Grove was part of Mission San Diego de Alcalá, one of the Spanish missions in California. After Mexico became independent from Spain, the Californios (residents of Alta California) ranched on various land grants. The area that now includes Lemon Grove was granted to Santiago Argüello, who received more than 59,000 acres.
The first proprietor of Lemon Grove, Robert Allison, arrived in the region in 1850, coming from Sacramento. He purchased thousands of acres from Santiago Argüello's heirs; this land eventually became Lemon Grove, La Mesa, Encanto, and part of Spring Valley. Allison became a director and stockholder of the San Diego and Cuyamaca Railroad in 1886 and built the Allison Flume. Allison's son Joseph filed subdivision maps for "Lemon Grove" in 1892.