Auburn is a city in Sangamon County, Illinois, United States. The population was 4,771 at the 2010 census, and 4,681 in 2018. It is part of the Springfield, Illinois Metropolitan Statistical Area.
Auburn is located at 39°35′20″N 89°44′45″W (39.588969, -89.745962).
According to the 2010 census, Auburn has a total area of 4.08 square miles (10.57 km2), all land.
At the 2000 census there were 4,317 people in 1,618 households, including 1,187 families, in the city. The population density was 1,368.0 people per square mile (527.5/km²). There were 1,753 housing units at an average density of 555.5 per square mile (214.2/km²). The racial makeup of the city was 98.36% White, 0.30% African American, 0.16% Native American, 0.28% Asian, 0.30% from other races, and 0.60% from two or more races. Hispanic or Latino of any race were 0.76%.
Of the 1,618 households 42.0% had children under the age of 18 living with them, 56.6% were married couples living together, 13.2% had a female householder with no husband present, and 26.6% were non-families. 22.9% of households were one person and 9.7% were one person aged 65 or older. The average household size was 2.63 and the average family size was 3.09.