San Luis is a city in Yuma County, Arizona, United States. The population was 15,322 at the 2000 census. It is part of the Yuma Metropolitan Statistical Area. San Luis, located in the southwest corner of the state directly adjacent to Mexico's Federal Highway 2, was the second fastest-growing place among all cities and towns in Arizona of any size from 1990 and 2000. According to 2006 Census Bureau estimates, the population of the city is 22,634.