Adams County is the westernmost county of the U.S. state of Illinois. As of the 2010 census, the population was 67,103. Its county seat is Quincy.
According to the U.S. Census Bureau, the county has a total area of 871 square miles (2,260 km), of which 855 square miles (2,210 km) is land and 16 square miles (41 km) (1.9%) is water.
As of the 2010 United States Census, there were 67,103 people, 27,375 households, and 17,677 families residing in the county. The population density was 78.5 inhabitants per square mile (30.3/km). There were 29,842 housing units at an average density of 34.9 per square mile (13.5/km). The racial makeup of the county was 93.7% white, 3.5% black or African American, 0.7% Asian, 0.2% American Indian, 0.4% from other races, and 1.6% from two or more races. Those of Hispanic or Latino origin made up 1.2% of the population. In terms of ancestry, 43.5% were German, 13.1% were Irish, 10.7% were American, and 8.7% were English.
Of the 27,375 households, 29.9% had children under the age of 18 living with them, 50.0% were married couples living together, 10.7% had a female householder with no husband present, 35.4% were non-families, and 30.1% of all households were made up of individuals. The average household size was 2.37 and the average family size was 2.94. The median age was 40.7 years.
The median income for a household in the county was $43,824 and the median income for a family was $55,791. Males had a median income of $38,830 versus $29,371 for females. The per capita income for the county was $24,308. About 8.3% of families and 12.3% of the population were below the poverty line, including 17.5% of those under age 18 and 8.1% of those age 65 or over.
Adams County Illinois neighborhoods include: Ashley Ave, Birdie Lane, Broadway/Ohio, Cambridge, Cedar, College-24th, Hickory Grove, Hidden Cove, Historic District, Melting Pot, Quincy, Reservoir Park, Riverview Westside, Robins Glen, Schildt Lane, Sheridan Estates, Southern View, Stone Crest, Talken Drive, Trinity Lakes