Ontario Peak is an 8,696-foot mountain in Southern California's San Gabriel Mountains, within the San Bernardino National Forest and the Cucamonga Wilderness. Named for the city of Ontario about 12 miles to the south, it first appeared in the United States General Land Office Forest Atlas in 1908. The usual route to the summit begins at Icehouse Canyon, follows Forest Service Trail 7W07 to Icehouse Saddle, and continues on the Ontario Peak Trail. At about 13 miles round trip with roughly 4,100 feet of elevation gain, the climb is a demanding hike and a notable ascent in this part of the range.