Loyalton is the only incorporated city in Sierra County, California. At the 2020 census, the population was 740. Many of the population are ranchers, loggers, former loggers, or suburbanites who have relocated from the San Francisco Bay Area, Sacramento, and growing Reno–Tahoe area.

Goodyears Bar is a census-designated place in Sierra County, California. Goodyears Bar is located along the North Yuba River and California State Route 49 3.25 miles (5.23 km) west-southwest of Downieville. Its population was 69 in 2020.

Pike is a census-designated place in Sierra County, California. It sits at an elevation of 1,050 m. Pike is 8.5 miles (13.7 km) west-southwest of Alleghany. The community was named after Pike County, Missouri. The population was 159 at the 2020 census.

Downieville is a census-designated place in and the county seat of Sierra County, California. Downieville is on the North Fork of the Yuba River, at an elevation of 2,966 feet (904 m). Downieville's population was 290 in 2020. The village built along the banks of two pristine spring and snowmelt-fed rivers is a year-round destination.

Sierra City is a small, picturesque mountain town located in the northern Sierra Nevada mountain range in Sierra County, Northern California. It's part of the Gold Country region and is nestled in a scenic area surrounded by forested mountains. Sierra City is a small town with a population of 221 at the 2010 census, making it a peaceful and close-knit community.

Alleghany is a small census-designated place in Sierra County, California in the Sierra Nevada. It is situated in the Gold Country and continues to be a significant locale for gold mining. The town is home to a post office, a bar, and a mining museum. The population was 30 at the 2010 census.

Verdi is a census-designated place in Sierra County, California. Verdi sits at an elevation of 5,315 feet (1,620 m). The 2020 United States census reported Verdi's population was 179. It is just across the state line from Verdi, Nevada and below the Verdi Range.

Sierraville is a census-designated place in Sierra County, California. It is at the southern end of the huge Sierra Valley which is used primarily as pasture and is also at the junction of California State Route 49 and California State Route 89 southwest of Loyalton. The population was 239 as of the 2020 census.

Sierra Brooks is a census-designated place in Sierra County, California. Sierra Brooks sits at an elevation of 5,180 feet (1,580 m). The 2020 United States census reported Sierra Brooks's population was 467.

Sattley, formerly known as Church's Corners, is a census-designated place in Sierra County, California, United States. Sattley is located on California State Route 49 and California State Route 89 southwest of Loyalton. Sattley had a population of 44 in 2020.