The biggest county in the United States is San Bernardino County, California, with a land area of 20,057 square miles (51,947 km2).
Jackson county is 100.6 square miles
Rockwall County: 129 square miles.
Lincoln County is 4 831 square miles.
Loudon County, TN: 247 square miles.Loudon County, VA: 521 square miles.
The area of Travis County is 989 square miles.
Meade County has an area of 3,482 square miles.
The answer will depend on county in which country.
Jackson county is 100.6 square miles
Fulton County, GA's area is 534.75 square miles.
Baldwin County, AL's area is 2,027 square miles.
Marquette County, Michigan is 3,425 square miles.
Onondaga County, NY is 806 square miles.
Darlington County, SC is 567 square miles.
Tillamook County, Oregon is 1,133 square miles.
Rockwall County: 129 square miles.
Lincoln County is 4 831 square miles.
Hennepin County, Minnesota is 606 square miles.