Petersburg is a city located in the state of Illinois within the United States. It serves as the county seat of Menard County and is situated on the bluffs and portions of the floodplain overlooking the Sangamon River. The city is also part of the Springfield, Illinois metropolitan area.
The population of Petersburg was recorded at 2,258 during the 2020 census, a figure that remained nearly unchanged from the 2010 census. Geographically, the city is situated approximately 2 miles (3 km) north of New Salem, which was the original location where Abraham Lincoln first settled to begin his career.