Monrovia is a city in the foothills of the San Gabriel Mountains in the San Gabriel Valley of Los Angeles County, California, United States. The population was 37,931 at the 2020 census. Monrovia has been used for filming TV shows, movies and commercials.

Monrovia is the fourth-oldest general-law city in Los Angeles County and the L.A. Basin (after Los Angeles, Santa Monica, and Pasadena, all now charter cities). Incorporated in 1887, it has grown from a sparse community of orange ranches to a residential community of beyond 37,000.

Around 500 BC, the Tongva, a band of Shoshonean-speaking Indians, established settlements in what is now the San Gabriel Valley. They were called the Gabrieliño Indians by further on Spanish missionaries, a tribe of Mission Indians. The Tongva were not farmers; they gathered wild seeds, berries, and natural world along rivers and in marshlands. Abundant oaks in the Valley, such as Coast Live Oak and Interior Live Oak, provided a staple of the Tongva diet: acorn mush made of boiled acorn flour.

In 1769, the Portolà expedition was the first recorded Spanish (or any European) land entrance and exploration of present-day California, then the Spanish colonial Las Californias Province of the Viceroyalty of New Spain (colonial México). In 1542, Juan Rodríguez Cabrillo claimed it from sea for the King of Spain. The expedition led by Gaspar de Portolà proceeded north from San Diego, passing through the area en route to Monterey Bay. Accompanying Portolà was Franciscan padre Juan Crespí, the expedition’s diarist. Much of what is known of further on California is from Crespi’s detailed descriptions.