Iroquois County is a county located in the northeast part of the U.S. state of Illinois. According to the 2010 census, it has a population of 29,718. It is the only county in the United States to be named Iroquois, after the American Indian people. The county seat is Watseka. The county is located along the border with Indiana.
According to the U.S. Census Bureau, the county has a total area of 1,119 square miles (2,900 km), of which 1,117 square miles (2,890 km) is land and 1.6 square miles (4.1 km) (0.1%) is water. It is the third-largest county in Illinois by land area and the fifth-largest by total area.
The northern border of the county is about 60 miles (97 km) south of the city of Chicago. The county is bordered on the east by the state of Indiana and its counties of Benton and Newton. To the north lies Kankakee County. Vermilion County, out of which Iroquois County was originally formed, lies to the south. To the west is Ford County.
The Iroquois River enters the county from Indiana and flows westward along the south side of the village of Iroquois, then along the north side of the city of Watseka, whereupon it veers to the north and joins the larger Kankakee River near the city of Kankakee in the county of the same name; the Kankakee River then flows into the Illinois River further to the northwest in Will County. Sugar Creek, further to the south, also flows from the east to the west, entering from Indiana east of Stockland; it passes through the south edge of Milford, is joined by Mud Creek coming up from the south, and winds to the north past the village of Woodland and meets the Iroquois River near Watseka.
The Iroquois County State Wildlife Area, a 2,400-acre (970 ha) state park, is located in the northeast corner of the county. There are also three nature preserves: Bonnie’s Prairie, Hooper Branch Savanna, and Loda Cemetery Prairie.
As of the 2010 United States Census, there were 29,718 people, 11,956 households, and 8,175 families residing in the county. The population density was 26.6 inhabitants per square mile (10.3/km). There were 13,452 housing units at an average density of 12.0 per square mile (4.6/km). The racial makeup of the county was 94.7% white, 0.8% black or African American, 0.3% Asian, 0.2% American Indian, 2.6% from other races, and 1.3% from two or more races. Those of Hispanic or Latino origin made up 5.3% of the population. In terms of ancestry, 36.5% were German, 14.1% were Irish, 12.2% were American, and 10.1% were English.
Of the 11,956 households, 30.2% had children under the age of 18 living with them, 54.7% were married couples living together, 9.3% had a female householder with no husband present, 31.6% were non-families, and 27.2% of all households were made up of individuals. The average household size was 2.45 and the average family size was 2.95. The median age was 43.4 years.
The median income for a household in the county was $47,323 and the median income for a family was $56,541. Males had a median income of $43,416 versus $27,908 for females. The per capita income for the county was $23,400. About 8.2% of families and 10.0% of the population were below the poverty line, including 14.1% of those under age 18 and 7.8% of those age 65 or over.