Santiago Dam (also known as Santiago Creek Dam) is an earth/rockfill dam across Santiago Creek in Orange County, in the U.S. state of California, forming Irvine Lake. The 136-foot (41 m) earth dam and its reservoir serve for flood control and recreational purposes. It lies upstream (southeast) from the city of Orange and north of Irvine. Irvine Lake is the largest body of fresh water entirely in Orange County.
Construction on the dam started in 1929 with a joint venture by the Irvine Company and Serrano Irrigation District. After the site was graded, the dam was built using dirt and rock excavated from the sides of the canyon and from the streambed both above and below the dam site. The structure was completed in 1931 at a cost of $1 million, and its reservoir, Irvine Lake, filled by 1933. In the late 1930s, the lake was stocked with fish, and was opened to the public for recreational use in 1941.