Approx 8163 square miles.
8,163 mi²
Kern County, CA covers 8,161 square miles.
There is no strict definition of "Southern California." But if you want to count LA County, San Diego County, Orange County, Riverside County, San Bernardino County, Ventura County, and Santa Barbara County; then Southern California is about 40,892 square miles. If you add in Kern County, San Luis Obispo County, and Imperial County...then Southern California is about 56,512 square miles.
Jackson County in Florida covers approximately 917 square miles.
Onondaga County, NY is 806 square miles.
Marquette County, Michigan is 3,425 square miles.
Darlington County, SC is 567 square miles.
Hennepin County, Minnesota is 606 square miles.
The smallest county in Texas is Rockwall County, which is about 147 square miles in size.
There are 2,569 square miles in Lincoln County, Nevada.
Tillamook County, Oregon is 1,133 square miles.
Fulton County, GA's area is 534.75 square miles.
Baldwin County, AL's area is 2,027 square miles.