The community was settled in 1869 by its first known permanent resident, sheep rancher Robert Allison. From the 1860s to 1900 the area was known for sheep and poultry ranching and vegetable crops. In the early 1900s, the community acquired its name when large citrus groves were planted, and lemon and orange growing and shipping became the area's major industry.
The Lemon Grove Incident in 1931 was a boycott of segregated schools by Mexican Americans, resulting in the first court-ordered school desegregation in the United States.
By World War II, most of the citrus groves had disappeared and suburbanization had begun. By 1960, most of the easily developable land was gone. Lemon Grove was incorporated as a general-law city in 1977; however, it continues to receive law enforcement services, via contract, from the San Diego County sheriff's office.
In 1966, two male teenagers ventured to caves near Chihuahua, Mexico, in search of a mummy to keep for their own. After spending more than a month exploring caves, the teens finally found two mummies, which they packed up and smuggled across the border.
Having no idea what to do with their discoveries and not wanting their parents to know, the teens asked a friend if they could store a box in her garage in Lemon Grove, California.
For 14 years, the mummies of the girl and the infant remained in the Lemon Grove garage, until the mother of the friend began to clean out her garage. The mother discovered the mummies and as a result believed a murder had taken place. When the mummies were tracked back to the two males, they wanted to donate the mummies to a museum. San Diego Museum of Man officials contacted Mexican authorities and asked for permission to keep the mummies as exhibits and an addition to the permanent collection. Permission was granted, and the mummies were placed on exhibit.
According to the United States Census Bureau, the city has a total area of 9.8 km² (3.8 mi²), all land.
As of the census of 2000, there were 24,918 people, 8,488 households, and 5,958 families residing in the city. The population density was 2,531.8/km² (6,557.3/mi²). There were 8,722 housing units at an average density of 886.2/km² (2,295.2/mi²). The racial makeup of the city was 59.63% White, 12.08% African American, 1.10% Native American, 5.75% Asian, 0.84% Pacific Islander, 13.50% from other races, and 7.10% from two or more races. Hispanic or Latino of any race were 28.52% of the population.
There were 8,488 households out of which 36.4% had children under the age of 18 living with them, 49.0% were married couples living together, 15.6% had a female householder with no husband present, and 29.8% were non-families. 22.4% of all households were made up of individuals and 8.9% had someone living alone who was 65 years of age or older. The average household size was 2.87 and the average family size was 3.36.
In the city the population was spread out with 27.6% under the age of 18, 9.0% from 18 to 24, 30.9% from 25 to 44, 20.5% from 45 to 64, and 12.0% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 93.9 males. For every 100 females age 18 and over, there were 91.0 males.
The median income for a household in the city was $39,823, and the median income for a family was $45,844. Males had a median income of $35,042 versus $28,509 for females. The per capita income for the city was $17,002. About 9.2% of families and 13.7% of the population were below the poverty line, including 18.0% of those under age 18 and 5.9% of those age 65 or over.
According to estimates by the San Diego Association of Governments, the median household income of Lemon Grove in 2005 was $55,436 (not adjusted for inflation). When adjusted for inflation (1999 dollars; comparable to Census data above), the median household income was $45,016.
In the state legislature Lemon Grove is located in the 39th Senate District, represented by Democrat Christine Kehoe, and in the 78th Assembly District, represented by Marty Block, a Democrat. Federally, Lemon Grove is located in California's 53rd congressional district, which has a Cook PVI of D +12 and is represented by Democrat Susan Davis.
There is a ten-foot-wide statue of a lemon located at 3361 Main Street. It lies before a small lemon grove beside the Orange Line Trolley tracks near the local Trolley station and downtown bus stop. Written across the base of this monument are the words "Best Climate On Earth".