According to the United States Census Bureau, the village has a total area of 6.4 square miles (16.6 km²), of which, 6.3 square miles (16.3 km²) of it is land and 0.1 square miles (0.3 km²) of it (1.87%) is water. South Elgin sits pretty in the pleasant Fox River Valley. Once populated by Native Indians South Elgin and the other boardering towns "Bartlett, Elgin & St. Charles" have done well in preserving this lands history. In 1811 and 1812 the Madrid fault cracked causing the largest earthquake in the history of the North American continent. It shook as far as the east coast as the bells in Boston rang for 4 minutes. The east coast experienced 6-7.0 shock waves from this midwest fault. The earthquake changed the geographic look to the midwest in some areas so bad that the Mississippi river ran backwards for 3 days. This destroyed a good amount of the Fox valley tribes as land slides and posinous waters spread disease threw the area. A few years later the French and Enlish went to war and invaded the Midwest thus killing most of the native Indians and or placing them in new locations as prisoners of war.
There were 5,565 households out of which 44.3% had children under the age of 18 living with them, 66.5% were married couples living together, 7.6% had a female householder with no husband present, and 22.6% were non-families. 17.1% of all households were made up of individuals and 3.0% had someone living alone who was 65 years of age or older. The average household size was 2.85 and the average family size was 3.26.
In the village the population was spread out with 29.1% under the age of 18, 6.9% from 18 to 24, 42.1% from 25 to 44, 16.1% from 45 to 64, and 5.7% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 100.2 males. For every 100 females age 18 and over, there were 96.0 males.
The median income for a household in the village was $67,323, and the median income for a family was $71,190. Males had a median income of $48,741 versus $31,486 for females. The per capita income for the village was $25,676. About 2.1% of families and 3.0% of the population were below the poverty line, including 3.6% of those under age 18 and 2.3% of those age 65 or over.