Round Mountain is a census-designated place in Shasta County, California, United States. Its population is 160 as of the 2020 census, up from 155 from the 2010 census.

Round Mountain is located at 40°47′59″N 121°56′35″W / 40.79972°N 121.94306°W / 40.79972; -121.94306 (40.799633, -121.943058).

According to the United States Census Bureau, the CDP has a total area of 1.7 square miles (4.4 km²), of which 99.60% is land and 0.40% is water.

Round Mountain is the geographic center of the Achomawi and Atsugewi or "Pit River" first nation. The "Pit River" tribe has never signed a treaty with the federal government and remains a strong force of opposition to federal control.

Round Mountain is the home of Hill Country Health and Wellness Center, one of the most solvent clinics in California. It also has the highest awarded LEEDS construction certificates of any clinic in California. Hill Country maintains a large youth facility.

Some organic farmers in Round Mountain are members of the Shasta Regional Seed Cooperative and work together to maintain hundreds of heirloom food crops as well as bio-dynamic farming techniques. Many residents are off the grid, using hydroelectric, solar and wind resources for their home power. Some of these forward-thinking residents also maintain local crime-watch activities and network projects to advance the sustainability of the region.

A large electrical substation is in the area, and power lines (Path 66 and a set of connecting wires to Path 15) run through the town.

A second substation was planned, then canceled, in 2009, along with 650 miles (1,050 km) of electrical lines from central California thru Round Mountain and then northbound. This plan, called TANC (Transmission Authority of Northern California), was halted by citizens who produced presentations statewide, showing that Department of Energy data conflicted with the project's stated goals. This 1.4 billion dollar TANC project was stopped in about 90 days.