It is the only county in the United States to be named Iroquois, named for the American Indian Tribe.
2000 - 31,334 1990 - 30,787 1980 - 32,976 1970 - 33,532 1960 - 33,562 1950 - 32,348 1940 - 32,496 1930 - 32,913 1920 - 34,841 1910 - 35,543 1900 - 38,014 1890 - 35,167 1880 - 35,451 1870 - 25,782 1860 - 12,325 1850 - 4,149 1840 - 1,695
As of the census of 2000, there were 31,334 people, 12,220 households, and 8,712 families residing in the county. The population density was 28 people per square mile (11/km²). There were 13,362 housing units at an average density of 12 per square mile (5/km²). The racial makeup of the county was 95.93% White, 0.71% Black or African American, 0.17% Native American, 0.30% Asian, 0.02% Pacific Islander, 2.07% from other races, and 0.79% from two or more races. 3.88% of the population were Hispanic or Latino of any race. 36.4% were of German, 12.0% American, 8.7% English, 8.1% Irish and 7.0% French ancestry according to Census 2000. 95.3% spoke English, 3.0% Spanish and 1.1% German as their first language.
There were 12,220 households out of which 31.30% had children under the age of 18 living with them, 59.20% were married couples living together, 8.50% had a female householder with no husband present, and 28.70% were non-families. 25.20% of all households were made up of individuals and 13.40% had someone living alone who was 65 years of age or older. The average household size was 2.51 and the average family size was 2.99.
In the county the population was spread out with 25.40% under the age of 18, 7.10% from 18 to 24, 25.70% from 25 to 44, 23.60% from 45 to 64, and 18.10% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 96.20 males. For every 100 females age 18 and over, there were 91.80 males.
The median income for a household in the county was $38,071, and the median income for a family was $45,417. Males had a median income of $31,799 versus $20,936 for females. The per capita income for the county was $18,435. About 6.80% of families and 8.70% of the population were below the poverty line, including 11.80% of those under age 18 and 6.70% of those age 65 or over.