Alleghany is a small census-designated place in Sierra County, California, United States in the Sierra Nevada. It is situated in the Gold Country and continues to be a significant locale for gold mining. The 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, 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 km), all of it land.

Historical population

Census	Pop.	Note	%±
2020	30		—
U.S. Decennial Census 1850–1870 1880-1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

The 2010 United States Census reported that Alleghany had a population of 58. The population density was 166.2 inhabitants per square mile (64.2/km). The racial makeup of Alleghany was 58 (100.0%) White. Hispanic or Latino of any race were 1 persons (1.7%).

The Census reported that 58 people (100% of the population) lived in households, 0 (0%) lived in non-institutionalized group quarters, and 0 (0%) were institutionalized.

There were 27 households, out of which 5 (18.5%) had children under the age of 18 living in them, 12 (44.4%) were opposite-sex married couples living together, 3 (11.1%) had a female householder with no husband present, 2 (7.4%) had a male householder with no wife present. There were 5 (18.5%) unmarried opposite-sex partnerships, and 0 (0%) same-sex married couples or partnerships. 5 households (18.5%) were made up of individuals, and 1 (3.7%) had someone living alone who was 65 years of age or older. The average household size was 2.15. There were 17 families (63.0% of all households); the average family size was 2.35.

The population was spread out, with 8 people (13.8%) under the age of 18, 2 people (3.4%) aged 18 to 24, 5 people (8.6%) aged 25 to 44, 36 people (62.1%) aged 45 to 64, and 7 people (12.1%) who were 65 years of age or older. The median age was 53.0 years. For every 100 females, there were 123.1 males. For every 100 females age 18 and over, there were 117.4 males.

There were 40 housing units at an average density of 114.6 per square mile (44.2/km), of which 16 (59.3%) were owner-occupied, and 11 (40.7%) were occupied by renters. The homeowner vacancy rate was 5.9%; the rental vacancy rate was 0%. 37 people (63.8% of the population) lived in owner-occupied housing units and 21 people (36.2%) lived in rental housing units.

In the state legislature, Alleghany is in the 1st Senate District, represented by Republican Brian Dahle, and the 1st Assembly District, represented by Republican Megan Dahle.

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

• Robert D. Walsh, U.S. Army brigadier general

• History of Sierra County, by James J. Sinnott, vol.3: Alleghany and Forest City: Treasure Towns, published by California Traveler, Volcano, California, 1975.
• Lode Deposits of the Alleghany District, California by Henry G. Ferguson, United States Geological Survey Bulletin #580, 1914.
• Gold Quartz Veins of the Alleghany District, California, by HG Ferguson and RW Gannett, US Geological Survey Professional Paper #172, 1932.

• Original Sixteen to One Mine website
• Underground Gold Miners of California Museum
• Pliocene Ridge Community Services District