According to the U.S. Census Bureau, the county has a total area of, of which is land and is water.
Climate and weather
In recent years, average temperatures in the county seat of Lawrenceville have ranged from a low of in January to a high of in July, although a record low of was recorded in January 1994 and a record high of was recorded in June 1988. Average monthly precipitation ranged from in February to in May.
As of the 2010 United States Census, there were 16,833 people, 6,130 households, and 4,056 families living in the county. The population density was. There were 6,936 housing units at an average density of. The racial makeup of the county was 87.3% white, 9.6% black or African American, 0.2% Asian, 0.2% American Indian, 1.7% from other races, and 1.0% from two or more races. Those of Hispanic or Latino origin made up 3.3% of the population. In terms of ancestry, 12.7% were German, 10.4% were American, 9.5% were Irish, and 7.8% were English. Of the 6,130 households, 28.6% had children under the age of 18 living with them, 50.7% were married couplesliving together, 10.7% had a female householder with no husband present, 33.8% were non-families, and 30.1% of all households were made up of individuals. The average household size was 2.34 and the average family size was 2.88. The median age was 39.7 years. The median income for a household in the county was $38,771 and the median income for a family was $45,565. Males had a median income of $40,949 versus $25,991 for females. The per capita income for the county was $19,297. About 14.8% of families and 17.5% of the population were below the poverty line, including 26.9% of those under age 18 and 7.7% of those age 65 or over.
In its early days, Lawrence County was a Democratic-leaning swing county, voting Republican only twice up to 1892 when it supported Ulysses S. Grant in 1872 and Benjamin Harrison in 1888. It did not vote for a losing Republican candidate until Wendell Willkie carried the county in 1940 due to isolationist sentiment. Since that time, however, Lawrence County – like so many in Southern Illinois – has become powerfully Republican due to opposition to Democratic Party social liberalism. The only Democrat to gain an absolute majority in the county since 1936 has been Lyndon Johnson in 1964, although Bill Clinton obtained pluralities in both 1992 and 1996.
