Winnebago County is a county located in the state of Illinois. As of 2000, the population is 278,418. Its county seat is Rockford, Illinois.
According to the U.S. Census Bureau, the county has a total area of 1,345 km² (519 mi²). 1,331 km² (514 mi²) of it is land and 14 km² (6 mi²) of it is water. The total area is 1.07% water.
Winnebago County was formed in 1836 out of Jo Daviess and LaSalle Counties. It was named for the Winnebago Tribe of Native Americans.
As of the census2 of 2000, there are 278,418 people, 107,980 households, and 73,642 families residing in the county. The population density is 209/km² (542/mi²). There are 114,404 housing units at an average density of 86/km² (223/mi²). The racial makeup of the county is 82.46% White, 10.53% Black or African American, 0.29% Native American, 1.72% Asian, 0.04% Pacific Islander, 3.11% from other races, and 1.86% from two or more races. 6.90% of the population are Hispanic or Latino of any race.
There are 107,980 households out of which 32.90% have children under the age of 18 living with them, 52.30% are married couples living together, 11.80% have a female householder with no husband present, and 31.80% are non-families. 26.30% of all households are made up of individuals and 9.60% have someone living alone who is 65 years of age or older. The average household size is 2.53 and the average family size is 3.06.
In the county the population is spread out with 26.40% under the age of 18, 8.40% from 18 to 24, 29.80% from 25 to 44, 22.70% from 45 to 64, and 12.70% who are 65 years of age or older. The median age is 36 years. For every 100 females there are 95.80 males. For every 100 females age 18 and over, there are 92.60 males.
The median income for a household in the county is $43,886, and the median income for a family is $52,456. Males have a median income of $40,289 versus $25,942 for females. The per capita income for the county is $21,194. 9.60% of the population and 6.90% of families are below the poverty line. Out of the total population, 12.90% of those under the age of 18 and 6.80% of those 65 and older are living below the poverty line.