Monte Rio (Spanish: Monte Río, meaning "River Mountain") is a census-designated place (CDP) in Sonoma County, California along the Russian River near the Pacific Ocean.

The town of Guerneville lies northeast of Monte Rio, and Jenner is to the west.

Starting in the 1870s, Monte Rio was a stop on the North Pacific Coast Railroad connecting Cazadero to the Sausalito, California ferry.

Redwood lumber from local sawmills was shipped to build San Francisco.

After the sawmills left, the area became known as Vacation Wonderland with trains transporting San Franciscans to summer cabins and even a seven-story hotel downtown.

[citation needed] Despite heavy logging during the second half of the 19th century, the Sonoma Lumber Company preserved a 160-acre (65 ha) grove of old-growth redwood trees, which was sold to San Francisco's Bohemian Club in 1899.

The club purchased dozens of other parcels in the area, and now owns 2,712 acres (1,098 ha), which are used for its summer retreats.

There were 930 housing units at an average density of 470.5 per square mile (181.7/km2), of which 56.9% were owner-occupied and 43.1% were occupied by renters.

In the California State Legislature, Monte Rio is in the 2nd Senate District, represented by Democrat Mike McGuire, and in the 2nd Assembly District, represented by Democrat Chris Rogers.