Lake Petersburg, Illinois

Lake Petersburg is a census-designated place in Menard County, Illinois, United States. Its population was 740 as of the 2020 census. The unincorporated community centers on a small reservoir, which is used extensively by residents for recreation.

Geography
Lake Petersburg is southwest of the center of Menard County, surrounding a reservoir of the same name, built in a valley that flows to the Sangamon River less than a mile to the east. Petersburg, the Menard county seat, is 2 mi to the north.

According to the U.S. Census Bureau, the Lake Petersburg CDP has a total area of 2.08 sqmi, within which the reservoir occupies 0.28 sqmi, or 13.2% of the community's area.