According to the United States Census Bureau, the city has a total area of 1.7 square miles (4.3 km²), all of it land.
There were 1,077 households out of which 31.1% had children under the age of 18 living with them, 53.7% were married couples living together, 9.8% had a female householder with no husband present, and 32.7% were non-families. 29.9% of all households were made up of individuals and 17.6% had someone living alone who was 65 years of age or older. The average household size was 2.36 and the average family size was 2.92.
In the city the population was spread out with 23.7% under the age of 18, 8.2% from 18 to 24, 24.3% from 25 to 44, 22.1% from 45 to 64, and 21.7% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 88.0 males. For every 100 females age 18 and over, there were 83.8 males.
The median income for a household in the city was $30,154, and the median income for a family was $37,368. Males had a median income of $33,194 versus $19,211 for females. The per capita income for the city was $16,340. About 6.4% of families and 9.0% of the population were below the poverty line, including 13.7% of those under age 18 and 8.2% of those age 65 or over.
Carrollton, Illinois is also the birthplace of Major Marcus Albert Reno who commanded a battalion of the 7th U.S. Cavalry at the Battle of the Little Bighorn. Many blamed Reno for Custer's defeat.
Carrollton, Illinois is also the birthplace and home of Henry Thomas Rainey who served as Speaker of the United States House of Representatives during the famous "100 Days" of Franklin Roosevelt's first term as president. Rainey died in 1934 and FDR came to his funeral in Carrollton.