Flat Rock is a village in Crawford County, Illinois, United States. The population was 331 at the 2010 census.
Flat Rock is located in southern Crawford County at 38°54′8″N 87°40′21″W / 38.90222°N 87.67250°W / 38.90222; -87.67250 (38.902220, -87.672402). Illinois Route 1 passes just west of the village, leading north 34 miles (55 km) to Marshall and south 12 miles (19 km) to Lawrenceville. Robinson, the Crawford County seat, is 10 miles (16 km) northwest of Flat Rock via IL 1 and IL 33.
According to the 2010 census, Flat Rock has a total area of 0.86 square miles (2.23 km), all land.
As of the census of 2000, there were 415 people, 166 households, and 118 families residing in the village. The population density was 485.0 people per square mile (186.3/km²). There were 176 housing units at an average density of 205.7 per square mile (79.0/km²). The racial makeup of the village was 96.63% White, 1.93% African American, 0.72% Asian, and 0.72% from two or more races.
There were 166 households out of which 31.9% had children under the age of 18 living with them, 59.6% were married couples living together, 7.8% had a female householder with no husband present, and 28.9% were non-families. 25.3% of all households were made up of individuals and 16.3% had someone living alone who was 65 years of age or older. The average household size was 2.50 and the average family size was 3.02.
In the village, the population was spread out with 24.3% under the age of 18, 8.9% from 18 to 24, 24.3% from 25 to 44, 23.4% from 45 to 64, and 19.0% who were 65 years of age or older. The median age was 38 years. For every 100 females, there were 89.5 males. For every 100 females age 18 and over, there were 89.2 males.
The median income for a household in the village was $36,184, and the median income for a family was $42,500. Males had a median income of $30,357 versus $15,417 for females. The per capita income for the village was $16,398. About 10.0% of families and 12.6% of the population were below the poverty line, including 23.5% of those under age 18 and 2.1% of those age 65 or over.