St. Augustine is a village in Knox County, Illinois, United States. The population was 120 at the 2010 census, down from 152 at the 2000 census. It is part of the Galesburg Micropolitan Statistical Area.
St. Augustine is located in the southwest corner of Knox County at 40°43′10″N 90°24′35″W / 40.71944°N 90.40972°W / 40.71944; -90.40972 (40.719523, -90.409832). The southern boundary of the village follows the Fulton county line. Illinois Route 41 passes through the center of the village, leading north 6 miles (10 km) to Abingdon and 17 miles (27 km) to Galesburg, the county seat. To the south IL 41 leads 14 miles (23 km) to Bushnell. Illinois Route 116 follows the northern border of the village, leading east 8 miles (13 km) to London Mills and west 13 miles (21 km) to Roseville.
According to the 2010 census, St. Augustine has a total area of 0.63 square miles (1.63 km), all land.
As of the census of 2000, there were 152 people, 68 households, and 43 families residing in the village. The population density was 247.2 people per square mile (96.2/km²). There were 73 housing units at an average density of 118.7 per square mile (46.2/km²). The racial makeup of the village was 100.00% White.
There were 68 households out of which 19.1% had children under the age of 18 living with them, 54.4% were married couples living together, 5.9% had a female householder with no husband present, and 35.3% were non-families. 27.9% of all households were made up of individuals and 14.7% had someone living alone who was 65 years of age or older. The average household size was 2.24 and the average family size was 2.75.
In the village, the population was spread out with 18.4% under the age of 18, 8.6% from 18 to 24, 20.4% from 25 to 44, 27.0% from 45 to 64, and 25.7% who were 65 years of age or older. The median age was 47 years. For every 100 females, there were 83.1 males. For every 100 females age 18 and over, there were 85.1 males.
The median income for a household in the village was $34,375, and the median income for a family was $35,357. Males had a median income of $27,500 versus $20,313 for females. The per capita income for the village was $15,549. About 4.3% of families and 5.6% of the population were below the poverty line, including none of those under the age of eighteen or sixty five or over.