Rancho Cucamonga () is a city located just south of the foothills of the San Gabriel Mountains and Angeles National Forest in San Bernardino County, California, United States. About 37 miles (60 km) east of Downtown Los Angeles, Rancho Cucamonga is the 26th most populous city in California. The city’s seal, which centers on a cluster of grapes, alludes to the city’s agricultural history including wine-making. The city’s proximity to major transportation hubs, airports, and highways has attracted the business of several large corporations, including Coca-Cola, Frito-Lay, Big Lots, Mercury Insurance Group, Southern California Edison, and Amphastar Pharmaceuticals.

The city had a population of 165,269 according to the 2010 United States Census and the Census Bureau estimated the population to be 177,603 in 2019. The city experiences an average of 287 sunny days per year, compared to a national average of 205 days. Its climate is classified as warm Mediterranean, or Csa, under the Köppen climate classification system.

The city’s favorable location and host of public amenities have earned it numerous distinctions. Notably, Money Magazine ranked Rancho Cucamonga 42nd on its “Best Places to Live” list in 2006. In addition, Business Insider established one Rancho Cucamonga neighborhood as the 13th richest neighborhood in Southern California. The four public high schools (Alta Loma, Etiwanda, Los Osos, and Rancho Cucamonga) earned the Silver distinction in a 2015 ranking of the nation’s high schools by U.S. News & World Report. In 2017 the California Department of Education announced that all four high schools were being named California Gold Ribbon Schools.

The Jack Benny Program popularized the city’s name, in particular the word “Cucamonga”.