[12] At the 2000 census there were 17,163 people, 6,974 households, and 4,791 families in the county.

The population density was 18 people per square mile (6.9 people/km2).

The racial makeup of the county was 98.76% White, 0.11% Black or African American, 0.15% Native American, 0.35% Asian, 0.01% Pacific Islander, 0.29% from other races, and 0.34% from two or more races.

Of the 6,974 households, 30.90% had children under the age of 18 living with them, 60.40% were married couples living together, 5.80% had a female householder with no husband present, and 31.30% were non-families.

Males had a median income of $30,191 versus $20,184 for females.

For use by the United States Census Bureau in population analysis, some of the rural population of Kossuth County has been grouped together as a Census-designated place.

The population ranking of the following table is based on the 2020 census of Kossuth County.