Tolay Lake is a shallow freshwater lake in southern Sonoma County, California, United States. The lake, nestled within the southern vestiges of the Sonoma Mountains, is the site of significant Native American prehistoric seasonal settlement. In 2005, Sonoma County acquired the entirety of the lake and virtually its whole drainage basin from the Cardoza family for the sum of $18 million; the County's intention is to utilize the property as Tolay Lake Regional Park for ecological and archaeological preservation, as well as public use and enjoyment.