Lake Mathews is a census-designated place in Riverside County, California, in the foothills of the Temescal Mountains between the cities of Riverside and Corona. The 2020 census counted 5,972 residents, and the community sits at an elevation of about 1,775 feet. The community takes its name from the reservoir that dominates its landscape. Lake Mathews, a large reservoir in Cajalco Canyon, was completed in 1939 as the western terminus of the Colorado River Aqueduct, the system that carries Colorado River water across the desert to the Metropolitan Water District's service area. Water was first delivered to the public in 1941, and the reservoir remains a critical piece of Southern California's municipal water supply, serving more than a million people across the region. Because Lake Mathews is a drinking-water reservoir, it is closed to public recreation, and its shoreline is not open for fishing or boating. The surrounding foothills, however, provide a scenic, semi-rural setting, with the Lake Mathews Ecological Reserve and nearby open space offering hiking, wildlife viewing, and sweeping views across the water. Public education is provided by two districts, reflecting the CDP's location across school boundaries: the Corona-Norco Unified School District and the Riverside Unified School District, the latter operating Lake Mathews Elementary School. Lake Mathews is a largely owner-occupied community of single-family homes on larger lots, with a semi-rural, equestrian-flavored character. Its position between Riverside and Corona gives residents easy access to employment, shopping, and the Inland Empire's freeway network, while the reservoir and foothills keep the community quieter and more spread out than its suburban neighbors.