Montgomery County is a county located in the U.S. state of Illinois. According to the 2010 census, it had a population of 30,104. Its county seat is Hillsboro.
According to the U.S. Census Bureau, the county has a total area of 710 square miles (1,800 km), of which 704 square miles (1,820 km) is land and 6.0 square miles (16 km) (0.8%) is water.
As of the 2010 United States Census, there were 30,104 people, 11,652 households, and 7,806 families residing in the county. The population density was 42.8 inhabitants per square mile (16.5/km). There were 13,080 housing units at an average density of 18.6 per square mile (7.2/km). The racial makeup of the county was 95.1% white, 3.2% black or African American, 0.4% Asian, 0.2% American Indian, 0.5% from other races, and 0.7% from two or more races. Those of Hispanic or Latino origin made up 1.5% of the population. In terms of ancestry, 27.8% were German, 11.2% were Irish, 10.1% were English, and 9.8% were American.
Of the 11,652 households, 29.8% had children under the age of 18 living with them, 51.7% were married couples living together, 10.2% had a female householder with no husband present, 33.0% were non-families, and 28.4% of all households were made up of individuals. The average household size was 2.38 and the average family size was 2.87. The median age was 41.9 years.
The median income for a household in the county was $40,864 and the median income for a family was $56,945. Males had a median income of $40,749 versus $29,426 for females. The per capita income for the county was $21,700. About 10.9% of families and 14.0% of the population were below the poverty line, including 22.7% of those under age 18 and 7.4% of those age 65 or over.