According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. It is the fourth-largest county in Illinois by land area.
Climate and weather
In recent years, average temperatures in the county seat of Pontiac have ranged from a low of in January to a high of in July, although a record low of was recorded in January 1927 and a record high of was recorded in July 1936. Average monthly precipitation ranged from in February to in June.
As of the 2010 United States Census, there were 38,950 people, 14,613 households, and 9,741 families residing in the county. The population density was. There were 15,895 housing units at an average density of. The racial makeup of the county was 91.8% white, 4.9% black or African American, 0.5% Asian, 0.2% American Indian, 1.3% from other races, and 1.3% from two or more races. Those of Hispanic or Latino origin made up 3.9% of the population. In terms of ancestry, 36.6% were German, 17.2% were Irish, 11.2% were American, 10.7% were English, and 5.1% were Italian. Of the 14,613 households, 30.7% had children under the age of 18 living with them, 52.0% were married couples living together, 9.9% had a female householder with no husband present, 33.3% were non-families, and 28.6% of all households were made up of individuals. The average household size was 2.43 and the average family size was 2.98. The median age was 40.8 years. The median income for a household in the county was $50,500 and the median income for a family was $60,933. Males had a median income of $44,639 versus $32,234 for females. The per capita income for the county was $23,259. About 9.1% of families and 11.0% of the population were below the poverty line, including 15.4% of those under age 18 and 6.9% of those age 65 or over.
Although it was solidly Democratic before 1856, Livingston has since always been a powerfully Republican county. The solitary Democrat to win a majority of the county's vote since the Civil War has been Franklin D. Roosevelt in his 1932 landslide triumph over Herbert Hoover. Apart from that and the 1912 election when Woodrow Wilson won against a mortally divided Republican Party, Livingston has always voted Republican since that party was founded in 1856. Since 1940, only Lyndon Johnson in his 1964 landslide victory over the conservative Barry Goldwater has won more than forty percent of the county's vote.
Francis Townsend, physician and political activist whose advocacy for an old age revolving pension influenced the creation of the U.S. Social Security program.
