Whiteside County is a county located in the U.S. state of Illinois. According to the 2010 census, it had a population of 58,498. Its county seat is Morrison. The county is bounded on the west by the Mississippi River.
According to the U.S. Census Bureau, the county has a total area of 697 square miles (1,810 km), of which 684 square miles (1,770 km) is land and 12 square miles (31 km) (1.8%) is water.
As of the 2010 United States Census, there were 58,498 people, 23,740 households, and 16,005 families residing in the county. The population density was 85.5 inhabitants per square mile (33.0/km). There were 25,770 housing units at an average density of 37.7 per square mile (14.6/km). The racial makeup of the county was 92.2% white, 1.3% black or African American, 0.5% Asian, 0.3% American Indian, 3.5% from other races, and 2.2% from two or more races. Those of Hispanic or Latino origin made up 11.0% of the population. In terms of ancestry, 32.5% were German, 15.5% were Irish, 8.7% were Dutch, 8.6% were English, and 6.0% were American.
Of the 23,740 households, 30.4% had children under the age of 18 living with them, 51.5% were married couples living together, 11.0% had a female householder with no husband present, 32.6% were non-families, and 27.7% of all households were made up of individuals. The average household size was 2.42 and the average family size was 2.92. The median age was 41.8 years.
The median income for a household in the county was $45,266 and the median income for a family was $54,242. Males had a median income of $41,862 versus $29,157 for females. The per capita income for the county was $23,405. About 8.2% of families and 11.2% of the population were below the poverty line, including 17.6% of those under age 18 and 5.8% of those age 65 or over.