The town is 20 miles (32 km) from the nearest highway (California State Route 49) and consists largely of a single main street.

The community was named in 1859 for the Alleghany Tunnel mine that fueled the growth of the town when it struck gold four years earlier.

[3] According to the United States Census Bureau, the CDP covers an area of 0.3 square miles (0.9 km2), all of it land.

There were 40 housing units at an average density of 114.6 per square mile (44.2/km2), of which 16 (59.3%) were owner-occupied, and 11 (40.7%) were occupied by renters.

[22] Federally, Alleghany is in California's 1st congressional district, represented by Republican Doug LaMalfa.