According to the U.S. Census Bureau, the county has a total area of 52,073 km² (20,105 mi²). 51,936 km² (20,052 mi²) of it is land and 137 km² (53 mi²) of it is water. The total area is 0.26% water. It is the largest county in the lower 48 states, and is thirteen times the area of the state of Rhode Island.

As of the census2 of 2000, there were 528,594 households, and 404,374 families residing in the county. The population density was 33/km² (85/mi²). There were 601,369 housing units at an average density of 12/km² (30/mi²). The racial makeup of the county was 58.91% White, 9.09% African American, 1.17% Native American, 4.69% Asian, 0.30% Pacific Islander, 20.82% from other races, and 5.03% from two or more races. 39.16% of the population were Hispanic or Latino of any race.

The median income for a household in the county was $42,066, and the median income for a family was $46,574. Males had a median income of $37,025 versus $27,993 for females. The per capita income for the county was $16,856. 15.80% of the population and 12.60% of families were below the poverty line. 20.60% of those under the age of 18 and 8.40% of those 65 and older were living below the poverty line.

Neighboring areas include: Clark County, Nev.; Mohave County, Ariz. La Paz County, Ariz. Riverside County, Orange County; Los Angeles County, Kern County, and Inyo County. Incorporated communities include Adelanto, Apple Valley, Barstow, Big Bear Lake, Chino, Chino Hills, Colton, Fontana, Grand Terrace, Hesperia, Highland, Loma Linda, Montclair, Needles, Ontario, Rancho Cucamonga, Redlands, Rialto, San Bernardino, Twentynine Palms, Upland, Victorville, and Yucaipa.