Alleghany is a small census-designated place in Sierra County, California, United States in the Sierra Nevada mountains. It is situated in the Gold Country and continues to be a significant locale for gold mining. The famous Sixteen-to-One Mine has been in operation since the days of the California Gold Rush. The town is 20 miles (32 km) from the nearest highway (California State Route 49) and consists largely of a single main street. The town is home to a post office, a bar (Casey's Place), and a mining museum. The population was 58 at the 2010 census.
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. The mine itself was named for the Allegheny River.
According to the United States Census Bureau, the CDP covers an area of 0.3 square miles (0.9 km²), all of it land.