San Luis Río Colorado is a city and municipality located in the northwestern corner of the state of Sonora, Mexico. It serves as a significant geographic landmark, marking the state border with Baja California and situated on the international border with the United States, adjacent to San Luis, Arizona.
The city is the fourth-largest community in the state of Sonora, with a population of 176,685 as of the 2020 census. The surrounding municipality covers an area of 8,412.75 km² within the Sonoran Desert and is also ranked as the fourth-largest municipality in the state by population. It is located approximately 75 km from the city of Mexicali.