County. Cahokia became the seat of St. Clair County, named by and after Arthur St. Clair, the first territorial governor. When St. Clair County was enlarged in 1801 and 1809, Governor William Henry Harrison (and later territorial secretary and acting governor Nathaniel Pope) named the Cahokia Courthouse as the legal and governmental center of a sizeable area extending to the Canada–U.S. border. By 1814, other counties and territories had been organized, and St. Clair County became its current size. The county seat was moved to the more centrally located Belleville, Illinois (incorporated 1819 and as a city in 1850) when a local developer offered to donate land for a new county courthouse and seat. In the late 1950s, Cahokia annexed some population and territory, increasing its population by more than 15,000 in 1960. Geography Cahokia was located at . According to the 2010 census, Cahokia had a total area of , of which (or 94.95%) is land and (or 5.05%) is water. Climate Demographics As of the census of 2000, there were 16,391 people, 5,693 households, and 4,252 families residing in the village. The population density was . There were 6,213 housing units at an average density of . The racial makeup of the village was 58.28% White, 38.69% African American, 0.32% Native American, 0.38% Asian, 0.03% Pacific Islander, 0.73% from other races, and 1.56% from two or more races. Hispanic or Latino of any race were 2.25% of the population. There were 5,693 households, out of which 41.2% had children under the age of 18 living with them, 43.2% were married couples living together, 25.7% had a female householder with no husband present, and 25.3% were non-families. 20.9% of all households were made up of individuals, and 8.6% had someone living alone who was 65 years of age or older. The average household size was 2.84 and the average family size was 3.27. In 2010, the population dropped to 15,241, with 61.30% being African American and 34.5% of the population being white alone. In the village, the population was spread out, with 33.4% under the age of 18, 8.7% from 18 to 24, 29.4% from 25 to 44, 16.9% from 45 to 64, and 11.6% who were 65 years of age or older. The median age was 31 years. For every 100 females, there were 88.7 males. For every 100 females age 18 and over, there were 82.5 males.