Mount Hamilton, Mountain summit in Santa Clara County, United States

Mount Hamilton is a summit in the Diablo Range of Santa Clara County, reaching 4,265 feet (1,300 m) on a mile-long ridge whose other peaks carry astronomical names. Lick Observatory, the world's first permanently occupied mountain-top observatory, stands at the top, its white domes visible above the houses and trees of the valley below. The 19-mile Mt. Hamilton Road climbs from San Jose in three long ascents.

On August 26, 1861, geologist William H. Brewer invited the San Jose preacher Laurentine Hamilton on a trek to the summit while working on the first California Geological Survey. Brewer proposed naming the peak after Hamilton only after Josiah D. Whitney declined the honour. Brewer and Charles F. Hoffmann did not know the Spanish name Sierra de Santa Isabel, and the peak two miles southeast was later named Mount Isabel.

The mountain's astronomical naming runs through its ridge: peaks beside Mount Hamilton carry names such as Kepler, and the highest, Copernicus Peak, lies 0.8 miles northeast. The asteroid 452 Hamiltonia, discovered in 1899, was named after the mountain. At the main observatory building, free 15-minute guided tours show the Great Lick refracting telescope.

The 31 km Mount Hamilton Road, part of State Route 130, was built in 1875–76 for horse-drawn wagons hauling observatory materials; its grade seldom exceeds 6.5 percent. The climb from San Jose rises over 1,200 m in three long climbs, interrupted by descents into Grant Ranch County Park and across Smith Creek. Quimby Road is a shorter but considerably steeper alternative. Snow can fall from October through May.

The asteroid 452 Hamiltonia, discovered in 1899, is named after the mountain. Golden eagle nesting sites are found on its slopes, and on clear days the summit view reaches Mount Tamalpais, the Santa Cruz Mountains, Monterey Bay and even Yosemite National Park.