St. Jacob is a village in Madison County, Illinois, United States. The population was 1098 at the 2010 census.
St. Jacob is located at 38°43′1″N 89°46′2″W / 38.71694°N 89.76722°W / 38.71694; -89.76722 (38.716897, -89.767122).
According to the 2010 census, St. Jacob has a total area of 0.766 square miles (1.98 km), of which 0.76 square miles (1.97 km) (or 99.22%) is land and 0.006 square miles (0.02 km) (or 0.78%) is water.
As of the census of 2000, there were 801 people, 301 households, and 232 families residing in the village. The population density was 1,433.1 people per square mile (552.3/km²). There were 321 housing units at an average density of 574.3 per square mile (221.3/km²). The racial makeup of the village was 98.25% White, 0.50% Native American, 0.37% Asian, 0.50% from other races, and 0.37% from two or more races. Hispanic or Latino of any race were 1.75% of the population.
There were 301 households out of which 37.2% had children under the age of 18 living with them, 67.8% were married couples living together, 6.0% had a female householder with no husband present, and 22.9% were non-families. 19.6% of all households were made up of individuals and 9.0% had someone living alone who was 65 years of age or older. The average household size was 2.66 and the average family size was 3.01.
In the village, the population was spread out with 27.8% under the age of 18, 8.0% from 18 to 24, 30.3% from 25 to 44, 22.7% from 45 to 64, and 11.1% who were 65 years of age or older. The median age was 34 years. For every 100 females, there were 99.8 males. For every 100 females age 18 and over, there were 95.9 males.
The median income for a household in the village was $47,917, and the median income for a family was $55,417. Males had a median income of $36,000 versus $25,938 for females. The per capita income for the village was $20,340. About 3.3% of families and 9.7% of the population were below the poverty line, including 18.5% of those under age 18 and none of those age 65 or over.