San Bernardino County, officially the County of San Bernardino, is a county located in the southern portion of the U.S. state of California. As of the 2010 census, the population was 2,035,210, making it the fifth-most populous county in California, and the 12th-most populous in the United States.

With an area of 20,105 square miles, San Bernardino County is the largest county in the United States by area, although some of Alaska's boroughs and census areas are larger. It is larger than each of the nine smallest states, larger than the four smallest states combined, and larger than 70 sovereign nations.

Located in southeast California, this vast county stretches from where the bulk of the county population resides (in two Census County Divisions, holding 1,422,745 people as of the 2010 Census, covering the 450 square miles (1,166 km2)), across the thinly populated deserts and mountains. It spans an area from south of the San Bernardino Mountains in San Bernardino Valley, to the Nevada border and the Colorado River.