Santiago Creek is a major watercourse in Orange County in the U.S. state of California. About 34 miles (55 km) long, it drains most of the northern Santa Ana Mountains and is a tributary to the Santa Ana River. It is one of the longest watercourses entirely within the county.
Historically the Santiago Creek provided water for the Tongva Native American group, whose territory extended over much of northern present-Day Orange County and into the Los Angeles Basin. Native Americans have inhabited the Santiago Creek and Santa Ana River watershed for at least 12,000 years. The creek was named by the Spanish Gaspar de Portolá expedition of 1769, which crossed the Santa Ana River near the Santiago Creek confluence. A tributary of the creek was the subject of a short-lived silver boom in the 1870s. Present-day Santiago Peak shares its name with the creek. Irvine Lake dam was constructed in 1929, marking the end of the creek's free-flowing state. The creek now contributes a small amount to the municipal water supply of Orange County via pipelines from Irvine Lake.