Smithton is a village in St. Clair County, Illinois, United States. The population was 3,693 in the 2010 United States Census. It is part of the Metro East region of Greater Saint Louis.
Smithton is located at 38°24′21″N 89°59′33″W (38.405800, -89.992578).
The village has a total area of 3.86 square miles (10.0 km2), of which 3.82 square miles (9.9 km2) (or 98.96%) is land and 0.04 square miles (0.10 km2) (or 1.04%) is water., according to the 2010 census.
As of the census of 2000, there were 2,248 people, 786 households, and 605 families residing in the village. The population density was 1,344.5 people per square mile (519.7/km²). There were 807 housing units at an average density of 482.6 per square mile (186.6/km²). The racial makeup of the village was 97.46% White, 0.76% African American, 0.36% Native American, 0.40% Asian, 0.04% Pacific Islander, and 0.98% from two or more races. Hispanic or Latino of any race were 0.22% of the population.