Clay City is a village in Clay County, Illinois, United States. The population was 959 at the 2010 census. Clay City was named for the Kentucky statesman Henry Clay.
Clay City is located in southeastern Clay County at 38°41′13″N 88°21′11″W / 38.68694°N 88.35306°W / 38.68694; -88.35306 (38.686883, -88.353121), about 1 mile (1.6 km) southwest of the Little Wabash River. U.S. Route 50 passes through the southern side of the village, leading west 7 miles (11 km) to Flora and east 15 miles (24 km) to Olney. Louisville, the Clay County seat, is 14 miles (23 km) to the northwest.
According to the 2010 census, Clay City has a total area of 1.74 square miles (4.51 km), all land.
As of the census of 2000, there were 1,000 people, 436 households, and 262 families residing in the village. The population density was 561.0 people per square mile (216.9/km²). There were 486 housing units at an average density of 272.7 per square mile (105.4/km²). The racial makeup of the village was 99.40% White, 0.20% Native American, 0.10% Asian, and 0.30% from two or more races. Hispanic or Latino of any race were 0.40% of the population.
There were 436 households out of which 31.2% had children under the age of 18 living with them, 46.1% were married couples living together, 10.6% had a female householder with no husband present, and 39.9% were non-families. 35.6% of all households were made up of individuals and 18.1% had someone living alone who was 65 years of age or older. The average household size was 2.29 and the average family size was 2.98.
In the village, the population was spread out with 26.2% under the age of 18, 6.8% from 18 to 24, 26.9% from 25 to 44, 21.0% from 45 to 64, and 19.1% who were 65 years of age or older. The median age was 38 years. For every 100 females, there were 90.1 males. For every 100 females age 18 and over, there were 85.0 males.
The median income for a household in the village was $25,750, and the median income for a family was $33,750. Males had a median income of $25,417 versus $18,750 for females. The per capita income for the village was $13,776. About 12.3% of families and 16.4% of the population were below the poverty line, including 24.1% of those under age 18 and 6.2% of those age 65 or over.