Auburn is a city in Sangamon County, Illinois, United States. The population was 4,317 at the 2000 census, and 4,445 in 2009. It is part of the Springfield, Illinois Metropolitan Statistical Area.
Auburn is located at 39°35′20″N 89°44′45″W / 39.58889°N 89.74583°W / 39.58889; -89.74583 (39.588969, -89.745962).
According to the United States Census Bureau, the city has a total area of 3.2 square miles (8.2 km²), all of it land.