Lenzburg is a village in St. Clair County, Illinois, USA. The population was 521 at the 2010 census.
Lenzburg is located at 38°17′21″N 89°49′00″W.
According to the 2010 census, Lenzburg has a total area of 1.296 square miles (3.36 km2), of which 1.19 square miles (3.08 km2) (or 91.82%) is land and 0.106 square miles (0.27 km2) (or 8.18%) is water.
As of the census of 2000, there were 577 people, 217 households, and 169 families residing in the village. The population density was 467.2 people per square mile (179.7/km2). There were 235 housing units at an average density of 190.3 per square mile (73.2/km2). The racial makeup of the village was 99.13% White, 0.17% Native American, 0.17% Asian, and 0.52% from two or more races. Hispanic or Latino of any race were 0.69% of the population.
There were 217 households, out of which 36.4% had children under the age of 18 living with them, 53.5% were married couples living together, 18.4% had a female householder with no husband present, and 21.7% were non-families. 17.5% of all households were made up of individuals, and 8.3% 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 2.91.