Boone County is a county located in the state of Illinois. As of 2000, the population is 41,786. Its county seat is Belvidere, Illinois.
According to the U.S. Census Bureau, the county has a total area of 730 km? (282 mi?). 728 km? (281 mi?) of it is land and 2 km? (1 mi?) of it is water. The total area is 0.24% water.
As of the census of 2000, there are 41,786 people, 14,597 households, and 11,254 families residing in the county. The population density is 57/km? (149/mi?). There are 15,414 housing units at an average density of 21/km? (55/mi?). The racial makeup of the county is 90.09% White, 0.90% Black or African American, 0.29% Native American, 0.50% Asian, 0.01% Pacific Islander, 6.67% from other races, and 1.54% from two or more races. 12.49% of the population are Hispanic or Latino of any race.
There are 14,597 households out of which 40.10% have children under the age of 18 living with them, 64.20% are married couples living together, 8.70% have a female householder with no husband present, and 22.90% are non-families. 19.00% of all households are made up of individuals and 8.00% have someone living alone who is 65 years of age or older. The average household size is 2.84 and the average family size is 3.24.
In the county the population is spread out with 29.80% under the age of 18, 7.70% from 18 to 24, 29.90% from 25 to 44, 22.00% from 45 to 64, and 10.70% who are 65 years of age or older. The median age is 34 years. For every 100 females there are 100.20 males. For every 100 females age 18 and over, there are 97.60 males.
The median income for a household in the county is $52,397, and the median income for a family is $59,305. Males have a median income of $41,992 versus $25,695 for females. The per capita income for the county is $21,590. 7.00% of the population and 5.10% of families are below the poverty line. Out of the total population, 8.70% of those under the age of 18 and 5.80% of those 65 and older are living below the poverty line.